Add a one-block rank/select implementation for bitmaps

[fclaude]

Add a one-bock structure for rank/select on bitmaps, extending BitSequence.

[fclaude]

This is done, SelectPrev0/1 and SelectPrev0 could be optimized here.

[fclaude]

Also the access+rank operation can be implemented here faster.

[fclaude]

Stuff missing:

• access+rank (optimized version)
• SelectPrev0
• SelectPrev1
• SelectNext0
• Save
• Load

[fclaude]

Done with Save and Load. Included tests for it (this also tests the arrays).

Also done with access+rank (optimized versions)

Missing:

• SelectPrev0
• SelectPrev1
• SelectNext0

[fclaude]

Now we have more things missing:

• SelectPrev0
• SelectPrev1
• SelectNext0
• Select0/1 -- position-restricted version