[INTERNAL, API] Adds windows intrinsics and a generic implementation for bitScanReverse and bitScanForward.

Adds platform independent implementation for bitScanReverse and bitScanForward.
Changes result value for bit scan reverse and bit scan forward if no bit is set to length of the packed string.
Merge branch 'feature/fix_packed_string_bit_twiddling' of https://github.com/rrahn/seqan into feature/fix_packed_string_bit_twiddling

Conflicts:
	core/include/seqan/misc/misc_bit_twiddling.h