* Add explicit trigger characters for C (#4226)

* Stop completion before issuing subsequent requests (#4226)

Co-authored-by: Marios Sioutis <26476573+s-marios@users.noreply.github.com>

Add an `ALECompletePost` event along with everything needed to make it
useful for its primary purpose: fixing code after inserting completions.

* `ALEFix` can now be called with a bang (`!`) to suppress errors.
* A new `ALELintStop` command lets you stop linting, and start it later.

* Add autoimport support for deoplete

* Fix test_deoplete_source.py

* Use callback instead of is_async for deoplete

Shuogo, the author of Deoplete, does not recommend using the `is_async`
option:

> I think is_async is not recommended. It is not so useful and broken.
> You should use callback system instead.

Link: https://github.com/Shougo/deoplete.nvim/issues/1006#issuecomment-526797857

Incidentally, the same thread mentiones an issue started by w0rp:
https://github.com/Shougo/deoplete.nvim/issues/976

The deoplete docs also say is_async is deprecated:

> is_async        (Bool)
>     If the gather is asynchronous, the source must set
>     it to "True". A typical strategy for an asynchronous
>     gather_candidates method to use this flag is to
>     set is_async flag to True while results are being
>     produced in the background (optionally, returning them
>     as they become ready). Once background processing
>     has completed, is_async flag should be set to False
>     indicating that this is the last portion of the
>     candidates.
>
>     Note: The feature is deprecated and not recommended.
>     You should use callback system by
>     |deoplete#auto_complete()| instead.

Link: https://github.com/Shougo/deoplete.nvim/blob/master/doc/deoplete.txt

Co-authored-by: w0rp <w0rp@users.noreply.github.com>

Deoplete needs `get_complete_position` method and it has a different
signature. It already fetches the input string and attempts to detect
the position with `\k*` regexp patterns.

This option is used to determine if `min_pattern_length` is ignored.
In usual, it does not start completion when the matched input string is
shorter than `min_pattern_length`. But when the string matches
`input_pattern`, it starts completion even when ths string is `''`.

This reverts commit 975cc7af8fbabe234a220c84e56b7ff719d8d959.