Implement test plumbing for BitFifoItem tests...
Rename dataset generators in anticipation of BitFifoItem datasets.
Add tests for BitBuckets as items...  Failures for bytes & nibbles.
Distinguish between BitFifoItem::bit_capacity() and full_bit_capacity::<T>()
Add assert_le! macro which displays operands in failure information, unlike assert!
Simplify the assert failure format.
Remove an incorrect comment taken from cut'n'paste of assert_eq! definition.
Fix a bug in testing less-than-full-capacity pops of BitFifoItems.
Split out bitfifo, bitfifoitem, bitbucket and associated tests into separate files.
Add conventional top-level ./lib.rs with a clean set of exported items.
Update .gitignore because the new test binary has the unfortunate name "libtest~"