Respect user's set options when running original widget

Fixes GitHub #379

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

Releases/v0.5.0

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

Is executed immediately after sourcing the plugin

Should fix GitHub #334

Fixes #337

`stty` occasionally hangs (always in CircleCI) inside the async pty.

Disable the tests for now until we can figure out and fix/workaround
this issue.

Features/no overwrite config

Published at `ericfreese/zsh-autosuggestions-test`.

Contains:
- Ruby 2.5.3
- Supported zsh versions 4.3.11 through 5.6.2
- Test ruby dependencies

Also updates Circle CI config to use built docker image.

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

Is executed immediately after sourcing the plugin

From: https://raw.githubusercontent.com/CircleCI-Public/circleci-config-generator/9979b712033a072c3135aafb3c06e252c4e791f1/cci-config-generator.sh

Reset opts in some functions affected by GLOB_SUBST

Should fix GitHub #334

Fixes/async bad file descriptor

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

Update INSTALL.md

I lost myself in the internet abyss because of this imprecision. It might be helpful for the new noob trying to install that great tweak. :)

Improve completion suggestions

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.

Add install directions for Antigen

Fixes/no zpty

It is not available in zsh versions older than 5.3

Not needed after move away from zpty for async

Features/completion suggestions