BLD: New R versions require NAMESPACE file. Closes #1497.
Merge pull request #1504 from jseabold/namespace-for-r-package

BLD: New R versions require NAMESPACE file. Closes #1497.
TST: Test co2 load_data for Python 3.
BUG: Decode dates to strings.
Merge pull request #1505 from jseabold/to-datetime-py3

COMPAT: Make sure co2 load_data works for Python 3.
Merge pull request #1506 from bashtage/python-2-6-fixes

COMPAT: Fix format and decode errors in Python 2.6
ENH: Miniconda-based testing on Travis-CI

Experimental branch that uses miniconda rather than platform
python to test.  Has some advantages in that it is simple to reconfigure
alternative combinations of NumPy, SciPy, Cython and pandas easily,
at least as long as they are provided by Anaconda.