Support for mips/mipsel

Fix for issue #98

Avoid unaligned memory access on architectures that don't support it.
Fixed endianness related issues. 
Hi, James

I have checked out your 'SPARC' branch of htslib (https://github.com/jkbonfield/htslib/tree/SPARC) and it builds fine on mips/mipsel with all of the tests passing.

However, htslib from https://github.com/samtools/htslib/ is still failing to build from source on mips and mipsel.

I am will look into it and let you know what I found out.

Best Regards
Aleksandar Zlicic