Bad SMIRNOFF links

[dwhswenson]

Related to #114, #121 (etc.)

There are several other places that have the broken link (topology/smirnoff.html), the FAQ being one of the more problematic. Here's a search that finds them:

https://github.com/openforcefield/openforcefield.org/search?q=%22topology%2Fsmirnoff%22

Posting as a separate issue because it can fixed without fixing the details of getting a working stable docs build discussed in #121.

[jchodera]

Thanks for catching this, @dwhswenson!

[jchodera]

It appears that this was due to the decision to delete the topology branch, which also scrubbed it from the readthedocs page.

We can replace most of these with the RTD link for the latest SMIRNOFF specification should be:
https://open-forcefield-toolkit.readthedocs.io/en/latest/smirnoff.html

However, I think some of those items linked to the draft proposal, which would have been closer to this version which is no longer on readthedocs.

I'll fix these.

[davidlmobley]

Have these been fixed, @jchodera ?

[jchodera]

Whoops! Fixed here: #198