Layout helper improvements & documentation

- Fully documented layout helpers
- Rewrote tests for layout helpers to be more comprehensive and actually test the output.
- Fixed a few bugs in {{extend}} and {{block}} for fringe use cases.
Merge remote-tracking branch 'parent/master' into layouts-overhaul

Conflicts:
	README.md
Merge pull request #106 from ChiperSoft/master

Layout helper improvements & documentation