Mainly updated the grammars regarding the latest version of PEG.js.

# Updated dependencies in package definition

- for safety, I precised the main versions of the libraries used
- the dependency for PEG.js is not over GitHub anymore, since they released a new version in npm

The update to the latest PEG.js version required some changes in the grammars.

# Prepared support for alternative parsers

- improved the grammar builder function to be able to build several parsers per mode
- in AT-HTML mode, made the validator common to all parsers, by moving it a level up: it makes more sense and can be available for alternative parsers

Also, it's now the NodeInstancier instance which gives access to the Node class in the grammars, so that it could be made configurable at instancier creation.

# Other

- I also removed some old useless files by the way.
- I updated the duration limit of a test which was always failing on my machine (the performance impact is not big)