no need to load packages with `library` if added as `Depends` in DESCRIPTION file
no need for new environment, Quandl already has an own namespace BUT

setting the auth_code should be done like:

    Quandl$auth_token <- 'foobar'

Please mind the missing `r` at the end.
a `warning` might be more appropriate instead returning a character vector
DRY
no need to query start and end date if we have the `rows` parameter with the API
no need for trailing semicolons and separating commented parts
simplified R class check
simplified `if` conditions
DRY: no need for `pmatch` and creating freq2int helper as called multiple times
simplified conditional flow
simplified ts flow
change frequency computation for a simple switch instead of wizardry
check frequency based on name instead of index
typo
check provided params first
roxygenized - for more details please see:

 * https://github.com/yihui/roxygen2
 * https://github.com/hadley/devtools/wiki/Documenting-functions
fix: update url for authcode
do not `Depend` on packages not to clutter in global envir but `Import` from pacakges
add helper function to set Quandl API access token more easily
tweak readibility and update to R coding style standards, see e.g.

  * https://github.com/hadley/devtools/wiki/Style