Some people have gotten used to setting ZSH_AUTOSUGGEST_BUFFER_MAX_SIZE
to an empty string rather than leaving it unset. This lets them continue
to do that without getting any warnings (e.g. "bad math expression:
operand expected at end of string").

Based on https://github.com/Valodim/zsh-capture-completion

`zpty -r` with a pattern seems to have some funky behavior on older
versions, giving unpredictable results

Don't use `-s` option to `zmodload`. It is not available in zsh versions
older than 5.3

If running in sync mode and a completion takes a long time, the user can
^C out of it. We need to use `always` in the strategy function or the
pty will not be destroyed in this case and the next time we go to create
it, it will fail, making the shell unusable.

User can have many different completion styles set that will modify what
they've already typed. These styles will result in suggestions that
don't match what the user has already typed. We try our best to unset
some of the more problematic ones, but add some code to fetch to
invalidate suggestions that don't match what the user's already typed.

Addresses github #411

See technique used in `fast-syntax-highlighting`:
- ca2e18bbc9
- http://www.zsh.org/mla/users/2018/msg00424.html

Also see http://www.zsh.org/mla/users/2018/msg00432.html

In async response handler:
- We only want to read data in case of POLLIN or POLLHUP. Not POLLNVAL
  or select error.
- We always want to remove the handler, so it doesn't get called in an
  infinite loop when error is nval or err.

There is an upstream bug that prevents ctrl-c from resetting the prompt
immediately after a suggestion has been fetched asynchronously. A patch
has been submitted, but a workaround for now is to add `command true`
after the exec.

See https://github.com/zsh-users/zsh-autosuggestions/issues/364

Fixes GitHub #379

They're not quite ready. Keep them on a feature branch for now.

otherwise users are obliged to set the config values *after* sourcing
the plugin. They're not able to do it before. Also, re-sourcing the
plugin will reset the values to the defaults again.

See zimfw/zimfw#301

Fixes #335

Should fix GitHub #334

Fixes #337

otherwise users are obliged to set the config values *after* sourcing
the plugin. They're not able to do it before. Also, re-sourcing the
plugin will reset the values to the defaults again.

See zimfw/zimfw#301

Fixes #335

Should fix GitHub #334

We only want to read data in case of POLLIN or POLLHUP. Not POLLNVAL or
select error.

We always want to remove the handler, so it doesn't get called in an
infinite loop when error is nval or err.

In zsh source, see main zle event loop in zle_main.c raw_getbyte
function.

Should fix GitHub #353

To prevent the suggestion from not starting with the buffer string.

Example:

`ls / /[cursor left][cursor left]b`

Before the patch, suggests `ls /b /ls /bin/ /`

After the patch, suggests `ls /b /bin/`.

https://github.com/zsh-users/zsh-autosuggestions/issues/343#issuecomment-401675712

If running in sync mode and a completion takes a long time, the user can
^C out of it. Without this patch, the pty will not be destroyed in this
case and the next time we go to create it, it will fail, making the
shell unusable.

Just insert the first completion directly into the buffer and read the
whole buffer from the zpty.

It is not available in zsh versions older than 5.3

Not needed after move away from zpty for async

Error looked something like:

```
% echo 'f(zpty):8: unmatched '
_zsh_autosuggest_capture_completion:zpty:9: no such pty command: zsh_autosuggest_completion_pty
_zsh_autosuggest_capture_completion:zpty:14: no such pty command: zsh_autosuggest_completion_pty
_zsh_autosuggest_capture_completion:zpty:21: no such pty command: zsh_autosuggest_completion_pty
```

According to `man zshmodules`, the args to `zpty` are "concatenated with
spaces between, then executed as a command, as if passed to the eval
builtin." So we need to escape the `$` so that `$1` is passed to eval
instead of the value of `$1`.

https://github.com/zsh-users/zsh-autosuggestions/issues/341

See http://www.zsh.org/mla/users/2018/msg00432.html

See technique used in `fast-syntax-highlighting`:
- ca2e18bbc9
- http://www.zsh.org/mla/users/2018/msg00424.html

Fixes #337

`zpty -r` with a pattern seems to have some funky behavior on older
versions, giving unpredictable results

Need to make sure compinit is called in the pty or the shell hangs

Only a problem in synchronous mode

The `zsh -f` running in the PTY doesn't know about the non-exported
variables and functions defined in the original shell, thus can't make
suggestions for them. Run local functions in the PTY instead of a new
`zsh` process.

We have to handle things differently based on whether zle is active or
not (async vs. sync mode).

Only need the first completion result

Uses https://github.com/Valodim/zsh-capture-completion with some slight
modifications.