Added macro to prevent IndexOutOfBounds exception, added single value byte unpacker method and associated tests.
Get intToByte and longToByte working properly.

This commit builds on the work by flaviut to implement compile-time
checks for intToByte and longToByte. This commit does the following:

  1. Fix minor arithmetic error
  2. Compute offsets at compile-time when possible
  3. Perform run-time checks when necessary
Merge pull request #169 from non/topic/unpacker

Topic/unpacker