gfx: Refactor the Mac platform goop into platform/
Refactor the Linux font stuff
Remove native.rs. It's no longer needed; just use platform::* directly.
Remove some module aliases.

These aliases were there for old versions of resolve, and are no longer needed.
Refactor glyph.rs to modern Rust coding style
Refactor the HarfBuzz shaper to be in line with modern Rust style
Rename one of the two modules called "shaper"
Hoist all `extern mod` directives to the top level

This improves compile time and makes `use` directives look cleaner.
Nuke the TGA encoder
Add missing platform/mod.rs
Fix refactored code on linux.
Merge pull request #1 from metajack/refactor-gfx

Fix refactored code on linux.
Merge remote-tracking branch 'pcwalton/refactor-gfx'

Conflicts:
	src/servo-gfx/font.rs
	src/servo-gfx/font_context.rs
	src/servo-gfx/font_list.rs
	src/servo-gfx/freetype_impl/font_context.rs
	src/servo-gfx/image/encode/tga.rs
	src/servo-gfx/native.rs
	src/servo-gfx/platform/linux/font.rs
	src/servo-gfx/platform/linux/font_list.rs
	src/servo-gfx/platform/macos/font.rs
	src/servo-gfx/quartz/font_context.rs
	src/servo-gfx/quartz/font_list.rs
	src/servo-gfx/servo_gfx.rc
	src/servo-gfx/text/glyph.rs
	src/servo-gfx/text/mod.rs
	src/servo-gfx/text/shaper.rs
	src/servo-gfx/text/shaping/harfbuzz.rs
	src/servo-gfx/text/text_run.rs