Huge refactor: Use Silly file-system query engine.

Silly (https://github.com/ruhoh/silly) abstracts the core data-modeling logic used to model files and their metadata attributes (top metadata). It also implements the cascade. Finally it provides the query interface for finding all files relative to the cascade and also using constraints based on metadata.

Silly is now the engine that powers ruhoh but to get to this point, much of ruhoh had to be blown up. Now ruhoh's job is to provide a more opionated 'web-site' user interface. Namely user configuration files, data conversation (markdown) and templating langauges (mustache) and layout support. Additionally the web-based previewer, compiler, and asset-pipeline etc.

Sorry for the ultra massive commit but all of this was a proof-of-concept until finally it was working.
Pagination url is no longer customizable; remove test.
Paginator view is now a partial instead of a layout.
Add feature for parsing markdown in partials.
Add feature tests for custom data files + cascade.
Add support for ERB templates.

Note this is entirely enabled by Ruhoh::Views::Context which was implemented in the previous massive commit.
The context mixin acts as decoupled interface for the ruhoh templating environment, namely where collections can be automatically accessed via their name, e.g. 'essays.all.each { |a| a }'
Add support for HAML templates.