Link to RDocs.
Document helper methods in `MrDarcy` module.
Add docs to `MrDarcy::Context` and replace meta programming with `Forwardable`.
No docs for `MrDarcy::Promise`.
Add documentation to `MrDarcy::Deferred`, also replace metaprogramming with Forwardable and remove redundant block argument.
Nodoc for `MrDarcy::Drivers`.
Doc fixes.
Add docs for `MrDarcy::Drivers`...
Add heaps more documentation and replace more metaprogramming with forwardable.
Add requires where required.

* See what I did there?
Various test fixes to match recent refactors.
Bump to `0.4.2` - documentation & refactoring release.