Avoid requiring byteswapping functions

Instead of byteswapping a 32 bit word and writing it out as a
whole (which could even possibly lead to crashes due to
incorrect alignment on some platforms), write it out explicitly
in the intended byte order.

This avoids having to set a define indicating the endianness.
Make the deblocking handling endian independent

This avoids having to set a define indicating the endianness.

This doesn't incur any significant measurable slowdown.
Merge pull request #258 from mstorsjo/endian-cleanup

Avoid endian-specific code