feat(rely): add support for AMD module definitions

This commit rewrites the library from scratch.  Now supports AMD
style define() to define modules, and asynchronous require() calls.

BREAKING CHANGE:

Pretty much everything has changed...
chore(release): increment version number
chore(release): changelog
test: add more tests
fix: fix several bugs
feat(require): return self when called with 'rely'
chore(README): update readme
chore(release): increment version number
chore(release): changelog
Version 2.0.1