Now the code completely use the OOP library.

OOP: https://github.com/ymeine/oop

- added the OOP dependency to the package definition
- changed all class definitions to use the OOP library instead
- improved the `emphase` method thanks to the OOP's `dop` module: the options object accepts aliases for its properties
- improved code consistency to prepare a more OOP version of the library
- made the renderer instance callable: it calls its render method

WARNING: this code currently requires the OOP library to fix some things (issues have been reported: ymeine/oop#14, ymeine/oop#18)