Add ag flags based on ag 0.24.0.

* Added filetype completion with descriptions generated by parsing list-file-types.
* Added all other static flags not present.
Fix typo in _pgsql_utils --disable-dollar-quoting
virsh: make completion work with older versions of virsh

Older versions of virsh doesn't have the `--name` option. Moreover when
completing running domains, the title was "name domains" instead of
expected "running domains".
virsh: replace use of compadd with _describe

compadd is more low-level and doesn't setup completion descriptions
correctly. Notably, the description is not put in bold.
virsh: inactive domains don't have an ID
call vagrant directly to get hostnames/box names

-no longer makes the assumption that files are parseable, just call vagrant
    directly to get the information for status|box list
-cache results until Vagrantfile changes
pull latest bits from oh-my-zsh.git

-pulled in current _vagrant from oh-my-zsh.git
    https://github.com/robbyrussell/oh-my-zsh/blob/e7fdb028b52505947c7c3eb088586590f5b0b8cd/plugins/vagrant/_vagrant
Merge pull request #259 from lexinator/vagrant-improvments

call vagrant directly to get hostnames/box names
Merge pull request #258 from felixbuenemann/fix-pgsql-utils-typo

Fix typo in _pgsql_utils --disable-dollar-quoting
Add 'references' to candidates of migration field
Add '--exclude-pattern' option
Merge pull request #262 from mitukiii/rspec

Add '--exclude-pattern' option
Merge pull request #261 from mitukiii/rails

Add 'references' to candidates of migration field
Merge pull request #257 from vincentbernat/fix/virsh

Various virsh fixes
Merge pull request #249 from starcraftman/ag_add_completions

Add ag flags based on version 0.24.0.
_pip: removed to obey repo rules:
Upstream (as of 1.4.1) maintain it's own completion
(can be generated by pip/runner.py completion --zsh)

Fixes #194

Signed-off-by: Vadim A. Misbakh-Soloviov <mva@mva.name>
README.md: Fixing gentoo overlay info
README.md: Fixing gentoo overlay info