Merge pull request #10 from quandl/master

Merge back into develop
Preliminary tests added
Merge branch 'develop' of github.com:quandl/R-package into develop
tests added, weekly datasets accounted for, and columns are selectable
single dataset column selection bug fix
test file added
need to include libraries in test
Descriptive texts
Merge pull request #11 from quandl/develop

Develop