NEWS:
* Switching endianness mid-byte no longer potentially re-reads bytes.
* bit_offset now consistently refers to the number of bits already
  read.
* HParsedTokens now have a bit_length field; this is a size_t.  This
  may be removed for memory reasons.

The bit writer has not yet been updated to match; the result of
switching bit writer endianness in the middle of a byte remains
undefined.

Revert "C++ tests set up. They probably don't compile; need to write iostream ops for prettyprinting and set up C++ build in scons." Should have branched it.

This reverts commit 6a29277d.

C++ tests set up. They probably don't compile; need to write iostream ops for prettyprinting and set up C++ build in scons.