Add/Change tests about true/false/[]

Current implementation does not encode/decode [] as {bert, nil}, nor true
as {bert, true}, nor false as {bert, false}.
Fix encoding/decoding true/false/[]
Fix decoding small integers. closes #3

Bert.decode(Bert.encode(130)) was returning -126.
According to http://erlang.org/doc/apps/erts/erl_ext_dist.html#id85118,
small integers are just one unsigned 8 bit integer.
Merge branch 'fix_boolean_nil'
Merge remote-tracking branch 'billiob/master'

* billiob/master:
  Fix decoding small integers. closes #3
  Fix encoding/decoding true/false/[]
  Add/Change tests about true/false/[]