Bump version: 0.4.2

[ci skip]

Bump version: 0.3.7

[ci skip]

Bump version: 0.4.1

Remove unused import

- remove_momentum() returns the removed momentum.

- remove_momentum() removes the momentum event also.
- clear events for removed momenta.
- velocity() returns right result at exact time.
- fix floating-point inacurracy problem caused by intersection.
- referring_gauges -> _limited_gauges
- restore _limited_gauges when unpickling.
- is_inside() -> in_range()
- outside option -> outbound