* [#420] Add options to facilitate linting only in normal mode
ale_lint_on_text_changed:
Allow setting to 'insert' or 'normal' to lint when text is changed only in
insert or normal mode respectively.
ale_lint_on_insert_leave:
This flag can be set to 1 to enable linting when leaving insert mode.
* [#420] Test updated global options
Ale should
- bind to TextChanged events when g:ale_lint_on_text_changed = 1
- bind to TextChanged events when g:ale_lint_on_text_changed = 'always'
- bind to InsertLeave event when g:ale_lint_on_insert_leave = 1
