MAINT: Port genetic_code.py over to skbio
MAINT: Move genetic_code exceptions to exceptions

The Exception classes are centralized insied skbio.exceptions as opposed
to being in genetic_code.py.
TST: Fix test_Synonims using assertItemsEqual
TST: Remove assertContains and assertNotContains
TST/API: Remove deprecated class method name
MAINT: Change test method names to be lowercase
STY: Comply with PEP8 stylistic needs
STY: Fix things that autopep8 cannot do on its own
DOC: Add module level doc
STY: PEP8-ify
DOC: Clean docstrings and add example
MAINT: CodeSequence -> code_sequence
MAINT: StartCodonSequence -> start_codon_sequence
MAINT: Name -> name
MAINT: ID -> id
MAINT: Change method names to be lowercase
MAINT: Synonims -> synonims
MAINT: Codons & Anticodons -> codons & anticodons
STY: Fix PEP8 things
STY: Change exceptions to be py3 compatible