copyright fix
pep8 complaints
update to use frozenset
Refactor class-level members in sequence module

Class-level attributes are now static methods. This fixes a number of issues:

- removes the danger of accidentally defining static attributes (e.g., temporary variables used in a for loop)
- complement mapping can now access the gap alphabet, so we don't need to remember to update gap character info in two places
- users won't be able to accidentally update things like valid IUPAC characters, complement mapping, etc.
- removes some duplicate code involved in constructing a few of the members

Additionally, ```alphabet``` and ```gap_alphabet``` are now static members.

Fixes #154 #167.
fix a couple of docstrings
all staticmethods are now classmethods

Thanks for the input @gregcaporaso!
Add unit tests for static methods

Now I can sleep at night
Port flatten over to skbio

This implementation of flatten is much cleaner and faster than other of
the available alternatives.
Fix problems with the Trie documentation

There were a few missing things that needed to be changed to make the
documentation render correctly.

Fixes #170
Fix PEP8 annoyances
Merge branch 'master' of github.com:biocore/bipy into not_executed

Conflicts:
	skbio/core/tests/test_workflow.py
	skbio/core/workflow.py
set([]) -> set()
msg is now an instance variable
removing exec flag
fixed exception juggling
More elegant dictionary updates

Thanks @wasade!
pep8 shit
Merge pull request #169 from ElBrogrammer/issue-167

Refactor class-level members in sequence module
fixed broken doctests
Reremoved exec