`BitArray` missing functionality

[lorentey]

This is a reminder for to do items in the BitCollection module. Some of these should probably be done in 1.1.0.

Missing BitArray operations:

• Masking shifts within a slice of a bit array (incl. range expressions)
• Bit rotations, supporting rotating the entire array as well as rotating bits in a specific slice
• Bit reversals, supporting reversing the entire array as well as reversing bits in a specific slice
• Review & revise bitwise operations. It ought to be possible to e.g. to do a bitwise OR over bit array slices.

We also need more tests coverage and additional benchmarks / performance work.

[lorentey]

Rescheduling to 1.2, as this should not block shipping 1.1.