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.
BUG: Format and decode errors in Python 2.6

Fixes two small errors on Python 2.6
- Improper use of keyword arguments in format, e.g errors='strict'
- Improper use of position-less format string
Merge pull request #1506 from bashtage/python-2-6-fixes

COMPAT: Fix format and decode errors in Python 2.6