Replace storage implementation with Moneta gem for simple key/value storage

Replace storage implementation with Moneta gem for simple key/value storage

This way the support for many storage options is transferred to the Moneta gem.
Many methods were deprecated, since Moneta does not support them (yet):
- `each`, `keys` & `values`, `size` and `merge!` are gone
- page storage `uniq!`, `pages_linking_to` and `urls_linking_to` are gone too

Default storage uses an in memory LRU-Hash implementation (Moneta default) with a max of 1Gb by default (configurable via Moneta options)

## Work In Progress - TODO

- [X] Replace custom key/value storage with Moneta gem
- [X] Fix specs
- [ ] Redo cli tools with user land algorithms to replace missing page storage methods
- [ ] Write docs & examples on how to use, at the least, the already supported storage options
- [ ] *Maybe* submit PR to Moneta to add an `each` method in the storage that would support it