key is not an optional value on initialization of a Client

also pep8
pep8
implement a compatibility wrapper for old module
pep8
alias compatibility client to match old interface
tests around compatibilty interface
split integration type tests out into their own test suite.
match and extend method signatures from legacy api
testing additional interfaces
Merge pull request #4 from kissmetrics/legacy-compat

Implement a compatibility interface for the original module