add asciidoc filetype and update markdown filetype

Add Gentoo info to the README

Added taskpaper as a file type

Add Agda and improve TeX ignore support

This was probably a transcription error when moving the ignore matcher
code out of ripgrep core. Specifically, the override glob matcher should
not ignore directories if they don't match.

Fixes #206

Add .fish extension to fish shell

If a user hits Ctrl-C to exit out of a search in the middle of printing
a line, we don't want to leave the terminal colors screwed up for them.
Catch Ctrl-C using the ctrlc crate, obtain a stdout lock to ensure that
other threads don't continue writing after we do so, reset the terminal,
and exit the program.

Closes #119

Move all gitignore matching to separate crate.

This PR introduces a new sub-crate, `ignore`, which primarily provides a
fast recursive directory iterator that respects ignore files like
gitignore and other configurable filtering rules based on globs or even
file types.

This results in a substantial source of complexity moved out of ripgrep's
core and into a reusable component that others can now (hopefully)
benefit from.

While much of the ignore code carried over from ripgrep's core, a
substantial portion of it was rewritten with the following goals in
mind:

1. Reuse matchers built from gitignore files across directory iteration.
2. Design the matcher data structure to be amenable for parallelizing
   directory iteration. (Indeed, writing the parallel iterator is the
   next step.)

Fixes #9, #44, #45

update python types to include Cython files

Add zsh type