examples : add Vim plugin (#1131)

* Initial proof of concept Vim plugin

At present, this is likely only slightly better than feature parity with
the existing whisper.nvim

Known issues:
 Trailing whitespace
 Up to an existing length(5 seconds) of speech may be processed when
  listening is enabled
 CPU cycles are spent processing speech even when not listening.

Fixing these issues is likely dependent upon future efforts to create a
dedicated library instead of wrapping examples/stream

* Support $WHISPER_CPP_HOME environment variable

A minor misunderstanding of the whisper.nvim implementation resulted in
a plugin that was functional, but not a drop in replacement as it should
be now.

examples/whisper.nvim/whisper.vim

@@ -0,0 +1,117 @@
+" The current whisper ecosystem shows mighty powerful potential, but seems to
+" lack the required structure to make a speech to text plugin frictionless.
+" The most direct path forward will be to have a standalone library interfaced
+" with vim's libcall
+" Libcall only allows for a single argument(a string or number) and a single
+" output (always a string).
+" This... honestly fits well for common interactions as follows
+"  init(modelname) -> (null string for success or error message)
+"  unload(ignored) -> (null string for success or error message)
+"   likely never needed
+"  processCommand(newline separated commands string) -> commands
+"   Should have support for consecutive commands
+"  stream(maybe sentinel?) -> processed text.
+"
+" Support for streaming responses is desired, but care is needed to support
+" backtracking when more refined output is available.
+" Perhaps the greatest element of difficulty, speech input should be buffered
+" and it should be possible to 'rewind' input to mask latency and pivot off
+" modal changes. (If a command sends the editor to insert mode, stt should no
+" longer be limited by the command syntax)
+"
+" For now though, a simple proof of concept shall suffice.
+if !exists("g:whisper_dir")
+   let g:whisper_dir = expand($WHISPER_CPP_HOME)
+   if g:whisper_dir == ""
+      echoerr "Please provide a path to the whisper.cpp repo in either the $WHISPER_CPP_HOME environment variable, or g:whisper_dir"
+   endif
+endif
+if !exists("g:whisper_stream_path")
+   if executable("stream")
+      " A version of stream already exists in the path and should be used
+      let g:whisper_stream_path = "stream"
+   else
+      let g:whisper_stream_path = g:whisper_dir .. "stream"
+      if !filereadable(g:whisper_stream_path)
+         echoerr "Was not able to locate a stream executable at: " .. g:whisper_stream_path
+         throw "Executable not found"
+      endif
+   endif
+endif
+if !exists("g:whisper_model_path")
+   " TODO: allow paths relative the repo dir
+   let g:whisper_model_path = g:whisper_dir .. "models/ggml-base.en.bin"
+   if !filereadable(g:whisper_model_path)
+      echoerr "Could not find model at: " .. g:whisper_model_path
+      throw "Model not found"
+   endif
+endif
+let s:streaming_command = [g:whisper_stream_path,"-m",g:whisper_model_path,"-t","8","--step","0","--length","5000","-vth","0.6"]
+
+let s:listening = v:false
+let s:cursor_pos = getpos(".")
+let s:cursor_pos[0] = bufnr("%")
+let s:loaded = v:false
+func s:callbackHandler(channel, msg)
+   " Large risk of breaking if msg isn't line buffered
+   " TODO: investigate sound_playfile as an indicator that listening has started?
+   if a:msg == "[Start speaking]"
+      let s:loaded = v:true
+      if s:listening
+         echo "Loading complete. Now listening"
+      else
+         echo "Loading complete. Listening has not been started"
+      endif
+   endif
+   if s:listening
+      let l:msg_lines = split(a:msg,"\n")
+      let l:new_text = ""
+      for l:line in l:msg_lines
+         " This is sloppy, but will suffice until library is written
+         if l:line[0] == '['
+            let l:new_text = l:new_text .. l:line[28:-1] .. ' '
+         endif
+      endfor
+         let l:buffer_line = getbufoneline(s:cursor_pos[0],s:cursor_pos[1])
+      if len(l:buffer_line) == 0
+         " As a special case, an empty line is instead set to the text
+         let l:new_line = l:new_text
+         let s:cursor_pos[2] = len(l:new_text)
+      else
+         " Append text after the cursor
+         let l:new_line = strpart(l:buffer_line,0,s:cursor_pos[2]) .. l:new_text
+         let l:new_line = l:new_line .. strpart(l:buffer_line,s:cursor_pos[2])
+         let s:cursor_pos[2] = s:cursor_pos[2]+len(l:new_text)
+      endif
+      call setbufline(s:cursor_pos[0],s:cursor_pos[1],l:new_line)
+   endif
+endfunction
+
+function! whisper#startListening()
+   let s:cursor_pos = getpos(".")
+   let s:cursor_pos[0] = bufnr("%")
+   let s:listening = v:true
+endfunction
+function! whisper#stopListening()
+   let s:listening = v:false
+endfunction
+function! whisper#toggleListening()
+   let s:cursor_pos = getpos(".")
+   let s:cursor_pos[0] = bufnr("%")
+   let s:listening = !s:listening
+   if s:loaded
+      if s:listening
+         echo "Now listening"
+      else
+         echo "No longer listening"
+      endif
+   endif
+endfunction
+
+" Note this includes stderr at present. It's still filtered and helps debugging
+let s:whisper_job = job_start(s:streaming_command, {"callback": "s:callbackHandler"})
+" TODO: Check lifetime. If the script is resourced, is the existing
+" s:whisper_job dropped and therefore killed?
+if job_status(s:whisper_job) == "fail"
+   echoerr "Failed to start whisper job"
+endif