First pass at optimizing ale to autoload (#80)

* First pass at optimizing ale to autoload

First off, the structure/function names should be revised a bit,
but I will wait for @w0rp's input before unifying the naming style.
Second off, the docs probably need some more work, I just did some
simple find-and-replace work.

With that said, this pull brings major performance gains for ale. On my
slowest system, fully loading ale and all its code takes around 150ms.

I have moved all of ale's autoload-able code to autoload/, and in
addition, implemented lazy-loading of linters. This brings load time on
that same system down to 5ms.

The only downside of lazy loading is that `g:ale_linters` cannot be
changed at runtime; however, it also speeds up performance at runtime by
simplfying the logic greatly.

Please let me know what you think!

Closes #59

* Address Travis/Vint errors

For some reason, ale isn't running vint for me...

* Incorporate feedback, make fixes

Lazy-loading logic is much improved.

* Add header comments; remove incorrect workaround

* Remove unneeded plugin guards

* Fix lazy-loading linter logic

Set the wrong variable....

* Fix capitialization

autoload/ale/cursor.vim

@@ -0,0 +1,119 @@
+" Author: w0rp <devw0rp@gmail.com>
+" Description: Echoes lint message for the current line, if any
+
+" Return a formatted message according to g:ale_echo_msg_format variable
+function! s:GetMessage(linter, type, text) abort
+    let msg = g:ale_echo_msg_format
+    let type = a:type ==# 'E'
+    \   ? g:ale_echo_msg_error_str
+    \   : g:ale_echo_msg_warning_str
+    " Capitalize the 1st character
+    let text = toupper(a:text[0]) . a:text[1:-1]
+
+    " Replace handlers if they exist
+    for [k, v] in items({'linter': a:linter, 'severity': type})
+        let msg = substitute(msg, '\V%' . k . '%', v, '')
+    endfor
+
+    return printf(msg, text)
+endfunction
+
+" This function will perform a binary search to find a message from the
+" loclist to echo when the cursor moves.
+function! s:BinarySearch(loclist, line, column) abort
+    let min = 0
+    let max = len(a:loclist) - 1
+    let last_column_match = -1
+
+    while 1
+        if max < min
+            return last_column_match
+        endif
+
+        let mid = (min + max) / 2
+        let obj = a:loclist[mid]
+
+        " Binary search to get on the same line
+        if a:loclist[mid]['lnum'] < a:line
+            let min = mid + 1
+        elseif a:loclist[mid]['lnum'] > a:line
+            let max = mid - 1
+        else
+            let last_column_match = mid
+
+            " Binary search to get the same column, or near it
+            if a:loclist[mid]['col'] < a:column
+                let min = mid + 1
+            elseif a:loclist[mid]['col'] > a:column
+                let max = mid - 1
+            else
+                return mid
+            endif
+        endif
+    endwhile
+endfunction
+
+function! ale#cursor#TruncatedEcho(message) abort
+    let message = a:message
+    " Change tabs to spaces.
+    let message = substitute(message, "\t", ' ', 'g')
+    " Remove any newlines in the message.
+    let message = substitute(message, "\n", '', 'g')
+
+    " We need to turn T for truncated messages on for shortmess,
+    " and then then we need to reset the option back to what it was.
+    let shortmess_options = getbufvar('%', '&shortmess')
+
+    try
+        " Echo the message truncated to fit without creating a prompt.
+        setlocal shortmess+=T
+        exec "norm :echomsg message\n"
+    finally
+        call setbufvar('%', '&shortmess', shortmess_options)
+    endtry
+endfunction
+
+function! ale#cursor#EchoCursorWarning(...) abort
+    " Only echo the warnings in normal mode, otherwise we will get problems.
+    if mode() !=# 'n'
+        return
+    endif
+
+    let buffer = bufnr('%')
+
+    if !has_key(g:ale_buffer_loclist_map, buffer)
+        return
+    endif
+
+    let loclist = g:ale_buffer_loclist_map[buffer]
+
+    let pos = getcurpos()
+
+    let index = s:BinarySearch(loclist, pos[1], pos[2])
+
+    if index >= 0
+        let l = loclist[index]
+        let msg = s:GetMessage(l.linter_name, l.type, l.text)
+        call ale#cursor#TruncatedEcho(msg)
+    else
+        echo
+    endif
+endfunction
+
+let s:cursor_timer = -1
+
+function! ale#cursor#EchoCursorWarningWithDelay() abort
+    if s:cursor_timer != -1
+        call timer_stop(s:cursor_timer)
+        let s:cursor_timer = -1
+    endif
+
+    let s:cursor_timer = timer_start(10, function('ale#cursor#EchoCursorWarning'))
+endfunction
+
+if g:ale_has_required_features && g:ale_echo_cursor
+    augroup ALECursorGroup
+        autocmd!
+        autocmd CursorMoved,CursorHold * call ale#cursor#EchoCursorWarningWithDelay()
+    augroup END
+endif