Problem: The current shortnames are weird and hard to use/remember

### Problem Description

The current shortnames, such as `4/STANDARDIZE-DC` and `6/SWP` are hard to use and remember. Do you remember what DC or SWP stands for? Will you remember in a year?

### Proposal

In practice, we've actually been using things like BEP4, BEP-4, BEP 4, or BEP#4, because that's much easier to say and to look up. The proposal is just to make that the official "short" way that we reference BEPs.

I think the Python community already does this when they refer to their PEPs, such as PEP-8.

Let's just change all the "shortname" labels to say BEP-N, where N is the BEP number.

Let's also do some searches for "1/C4" and "2/COSS" and replace those with BEP-1 and BEP-2. I think those are the only two shortnames we ever actually used.

- [x] Update all references and shortnames in the `master` branch. See PR #51
- [x] Update all references and shortnames in unmerged pull requests, except for PR #57
- [ ] Update the references and shortnames in PR #57 (the one that creates BEP-11)