Add cspell Linter (#3981)

* Add cspell linter

Add cspell linter, with the languages it supports.

Signed-off-by: David Houston <houstdav000@gmail.com>

* Add cspell Global Variables Documentation

Add documentation to /doc/ale.txt with cspell configuration options.

Signed-off-by: David Houston <houstdav000@gmail.com>

* Add cspell to docs, Minor Cleanup

Add cspell for each supported language, adding some spaces and removing
others when caught navigating the file.

Signed-off-by: David Houston <houstdav000@gmail.com>

autoload/ale/handlers/cspell.vim

@@ -0,0 +1,54 @@
+scriptencoding utf-8
+" Author: David Houston <houstdav000>
+" Description: Define a handler function for cspell's output
+
+function! ale#handlers#cspell#GetExecutable(buffer) abort
+    return ale#path#FindExecutable(a:buffer,
+    \    'cspell', [
+    \        'node_modules/.bin/cspell',
+    \        'node_modules/cspell/bin.js',
+    \    ]
+    \)
+endfunction
+
+function! ale#handlers#cspell#GetCommand(buffer) abort
+    let l:executable = ale#handlers#cspell#GetExecutable(a:buffer)
+    let l:options = ale#Var(a:buffer, 'cspell_options')
+
+    return ale#node#Executable(a:buffer, l:executable)
+    \   . ' lint --no-color --no-progress --no-summary'
+    \   . ale#Pad(l:options)
+    \   . ' -- stdin'
+endfunction
+
+function! ale#handlers#cspell#Handle(buffer, lines) abort
+    " Look for lines like the following:
+    "
+    " /home/user/repos/ale/README.md:723:48 - Unknown word (stylelint)
+    let l:pattern = '\v^.*:(\d+):(\d+) - (.*)$'
+    let l:output = []
+
+    for l:match in ale#util#GetMatches(a:lines, l:pattern)
+        call add(l:output, {
+        \   'lnum': l:match[1] + 0,
+        \   'col': l:match[2] + 0,
+        \   'text': l:match[3],
+        \   'type': 'W',
+        \})
+    endfor
+
+    return l:output
+endfunction
+
+function! ale#handlers#cspell#DefineLinter(filetype) abort
+    call ale#Set('cspell_executable', 'cspell')
+    call ale#Set('cspell_options', '')
+    call ale#Set('cspell_use_global', get(g:, 'ale_use_global_executables', 0))
+
+    call ale#linter#Define(a:filetype, {
+    \   'name': 'cspell',
+    \   'executable': function('ale#handlers#cspell#GetExecutable'),
+    \   'command': function('ale#handlers#cspell#GetCommand'),
+    \   'callback': 'ale#handlers#cspell#Handle',
+    \})
+endfunction