Tightened bounds on sky walls.
WadName type instead of [u8] and Vec-s.

Painful yet important commit. Replaced the WadName type synonym (which required
the use of Vec<u8> and &[u8] occasionally and did not support Eq & Hashing) to
a real type which supports all that as well as painless str, String and &[u8]
conversions.

Added ```--load-all``` command line option which simply loads all levels and
quits. Useful for diagnostics, ensuring no level loading fails.

Fixed a typo in one of the texture names which prevented it to load correctly.
Spotted thanks to the new WadName class.
Decodable WadName. Fixed WadName Tests.
Fixed Mat4 tests.
Less noise in test builds. Moved some utils in own module.
Added serialize crate back fixing build.
Added toml dependency. Went back to official sdl2.
Added TOML wad metadata.

A lot of stuff was hardcoded in the original doom; instead of replicating that,
I'm moving all asset related data not stored in the WAD file into a separate
TOML file.

For now this only includes the sky to level mapping, but it will be where I
store thing type -> sprite mappings as well, for instance.
Added anim & thing metadata.
Animations read from meta.
Minor sky tiling fix.
Fixes for changes in rustc and sdl2.

* ```static``` changed to ```const``` as per this [RFC](https://github.com/rust-lang/meeting-minutes/blob/master/workweek-2014-08-18/static-and-const.md).
* ```move`` became a keyword so some renaming had to be done.
* bitflags moved from camel case to uppercase letters in sdl2.
Use new slicing syntax.
Explicit subtractions instead of unsigned negations.
Make use of lifetime elision.
Added mouse toggle key (backtick)
Fixed issue where fast-slow strobes were swapped
More lighting tweaks.
Bumped version to 0.0.7
New minor release 0.0.7:

* Added metadata file to handle hardcoded things in the orignal game.
* Read the correct sky for each level from metadata.
* Read animation frames from metadata.
* Fixed build issues on newest compiler and libraries.
* A bunch of lighting fixes that make it truer to the original.
* Use new rust 0.12 features: lifetime elision & slicing syntax.
* Replace broken wad name handling with a type WadName. Much cleaner WAD code
  as a result.

Merge branch 'release/0.0.7'