Merge pull request pydata#130 from davidastephens/rel021

REL: Release 0.2.1

Merge pull request pydata#107 from davidastephens/rel_020

Update version number to 0.2.0

Merge pull request pydata#41 from dstephens99/master

RELEASE: v0.1.1

Merge pull request pydata#1 from pydata/interval

ENH add interval kwarg to get_data_yahoo