Use strict semver parser by default, add loose parser extending strict
Bugfixes in expressions
Switch over public API to the new expressions
Revert tests to state in 2.x (929a8e57bafe243b5cae5f3b2a9ae65676d2850a)
Nicer style for the grammar parsers
Add support for nested expressions.

An Or expression can now be nested inside an And expression.
This allows to create all arbitrary expressions