Support for mips/mipsel

Fix for issue #98

Avoid unaligned memory access on architectures that don't support it.
Fixed endianness related issues. 
@jkbonfield , Could you please update the https://github.com/jkbonfield/htslib/tree/SPARC branch?
The status right now is: This branch is 8 commits ahead, 96 commits behind samtools:develop