Company Mode Contrib Layer

Adds a contrib layer that allows you to use Company-mode for autocomplete. Includes configuration for company-auctex, company-tern and extra special configuration for company-clang.

## Clang Support

Adds support for reading `.clang_complete` files for autocomplete, useful for projects that require special flags to build properly. This file is also hooked into flycheck so that the errors messages are things that are actually problems. (Example of .clang_complete file for Arduino project: https://github.com/trishume/PolyType/commit/3b8375e62324bdee53248a313f06ffed4c5daf5a)

## Company Auctex

This plugin is SUPER buggy (see readme changes to trishume-contrib) and only works when Auctex is installed so it is only activated when both the `company-mode` and `trishume` contrib layers are activated. It is better than the auto-complete auctex one though, because that one takes a full minute to open a completion popup.

## General Tweaks

Tab completion was disabled to stop it from interfering with yasnippet and indentation. If someone can fix this and make tab behave correctly and intelligently that would be cool, I tried for a few hours and failed.

Also changes the default solarized company faces, which are ugly as hell. There's also some general config like having the popup appear instantly, disabling it in markdown mode and changing the lighter.

**Note:** I thought this was a good candidate for a PR that actually deserves to have multiples commits instead of being squashed. But I can squash it if you want.