BitMagic release v7.11.2

Bug fixes:

1. Fixed bug in rank-select index assisted compute of rank (affecting compressive sparse vector)
2. Fixed bug with potential misaligned reads in SIMD mode
3. Fixed bug in deserialization of empty sparse vector

New features and improvements:

1. Improved read-only mode for bm::bvector<> to allocate one contiguos memory block for the arena to
   better reduce memory fragmentation. This improvement also affects read-only mode memory allocation
   for bit-vector based succinct vectors.

2. succinct vector for strings (bm::str_sparse_vector) remap() method improved to use less memory
   in the process

3. Added bit-vector immutability methods into C-language mappings

Release notes:
http://bitmagic.io/bm-7.11.2.html