v2.5.0: cleanup

A small cleanup:

• Improving linting level.
• Some small fixes in phpdocs.
• No changes in function declarations. Leaving that to another major version.
• Nicer exceptions when passing invalid data to some functions, which already threw 'unknown method' exceptions.

Bumping minor version because there are a few new interface you could use if you're building own objects and documents.

This is last release before a new major, moving to new php version and stricter typing.