Add ALEStartLint autocmd

This grew out of my work in #1193; to ensure the statusline was being
updated I had to add:

    fun! s:redraw(timer)
        redrawstatus
    endfun

    augroup ALEProgress
        autocmd!
        autocmd BufWritePost * call timer_start(100, function('s:redraw'))
        autocmd User ALELint redrawstatus
    augroup end

Which kind of works, but is ugly. With this, I can replace the
`BufWritePost` with:

    autocmd User ALEStartLint redrawstatus

Which is much better, IMHO.

Actually, this patch actually replaces adding a function, since you can
do:

    augroup ALEProgress
        autocmd!
        autocmd User ALEStartLint hi Statusline ctermfg=darkgrey
        autocmd User ALELint      hi Statusline ctermfg=NONE
    augroup end

or:

    let s:ale_running = 0
    let l:stl .= '%{s:ale_running ? "[linting]" : ""}'
    augroup ALEProgress
        autocmd!
        autocmd User ALEStartLint let s:ale_running = 1 | redrawstatus
        autocmd User ALELint      let s:ale_running = 0 | redrawstatus
    augroup end

Both seem to work very well in my testing.

No need to `ale#Statusline#IsRunning()` anymore, I think?

1 files changed, 6 insertions, 4 deletions

diff --git a/README.md b/README.md
index 89bcc255..0292d52c 100644
--- a/README.md
+++ b/README.md
@@ -40,7 +40,7 @@ formatting tools, and some Language Server Protocol and `tsserver` features.
     5. [How can I show errors or warnings in my statusline?](#faq-statusline)
     6. [How can I show errors or warnings in my lightline?](#faq-lightline)
     7. [How can I change the format for echo messages?](#faq-echo-format)
-    8. [How can I execute some code when ALE stops linting?](#faq-autocmd)
+    8. [How can I execute some code when ALE starts or stops linting?](#faq-autocmd)
     9. [How can I navigate between errors quickly?](#faq-navigation)
     10. [How can I run linters only when I save files?](#faq-lint-on-save)
     11. [How can I use the quickfix list instead of the loclist?](#faq-quickfix)
@@ -493,15 +493,17 @@ Will give you:
 
 <a name="faq-autocmd"></a>
 
-### 5.viii. How can I execute some code when ALE stops linting?
+### 5.viii. How can I execute some code when ALE starts or stops linting?
 
 ALE runs its own [autocmd](http://vimdoc.sourceforge.net/htmldoc/autocmd.html)
-event whenever has a linter has been successfully executed and processed. This
-autocmd event can be used to call arbitrary functions after ALE stops linting.
+events whenever has a linter is started and has been successfully executed and
+processed. This autocmd event can be used to call arbitrary functions before and
+after ALE stops linting.
 
 ```vim
 augroup YourGroup
     autocmd!
+    autocmd User ALEStartLint call YourFunction()
     autocmd User ALELint call YourFunction()
 augroup END
 ```