New FRED URL

[jhoodsmith]

Updated url to reflect the changes by fred.stlouisfed.org for downloading CSV.

[bashtage]

This looks right and the FRED tests pass

[bashtage]

Can you rebase on master? It should pass and then this can be merged.

[rsvp]

It is not clear whether the new URL scheme at FRED is stable.
For example, the default values on their qualifiers (see #435)
may change without notice to pandas_datareader users,
which will unexpectedly transform datasets.

The old URL is still operational, so it may be a good idea
to wait on the pull until the new FRED API is made "official."

[jhoodsmith]

For what it's worth, I agree with @rsvp. The new code is there if needed, but for the time being I suggest we follow the 'if it ain't broke, don't fix' strategy. Thank you to @bashtage for fixing the testing suite though.

[bashtage]

The right way is https://research.stlouisfed.org/docs/api/fred/ but this requires an API key. The graph endpoint has been around for years and is used extensively through FRED to power the graphs.

[bashtage]

Accidental close.

[bashtage]

Also worth noting that this new endpoint is where data comes from when one interactively downloads data.

[bashtage]

I'm going to merge this. I think it is the right endpoint since it is where data comes from when it is manually downloaded and there is no officially supported one.