Gatenlp

* Several renames of API methods again:
* Annotation: boolean methods renamed to isxxx(), e.g. `ann1.within(ann2)` renamed to `ann1.iswithin(ann2)`
* AnnotationSet: some methods are now properties: `size`, `length`
* AnnotationSet: method `type(...)` renamed to `with_type(...)`

* Breaking change: `annset.add(..)` now returns the annotation, not just
the annotation id of the new annotation. This is more useful and getting
the id from the annotation is just `ann.id` while getting the annotation
from the annid is more involved.
* Breaking change: AnnotationSet methods where the annotation passed on would
get included in the result set because of the offset range, by default now
exclude that annotation. So `annset.within(ann1)` does not contain `ann1`
anymore, although `ann1` obviously satisfies the `within` criterion.
This can be disabled by passing `include_self=True` if necessary.