Previously the ale refresh was triggered after user interactions only.
When linting takes some time and the user is not actively working the
ale information was not updated while the things ale directly controls
were updated. This change makes showing linting results a loot smoother.
The function shows the line number of the first error/warning that appears in the current buffer. If there are 20 warnings and the first warning exists on line 33, then vim-airline would show "W:20(L33)".
One can change how the line number is represented using: `g:airline#extensions#ale#open_lnum_symbol` and `airline#extensions#ale#close_lnum_symbol`
