Standardize BIP/BOLT reference format

[andrei-21]

Problem

The guide is inconsistent when it labels Bitcoin Improvement Proposals and Lightning BOLTs:

• BIP-353 (with hyphen)
• BIP 21 (with space)
• BOLT12 (no space)

Proposal

Adopt the single, space-separated form already used by the RFC series: "BIP 21", "BOLT 12", etc.

Let me know if you agree and I will proceed with a PR.

[moneyball]

I don't have a strong view other than to just pick one, be consistent, and be influential throughout the ecosystem.

[GBKS]

Previously, we have reference the Bitcoin OpTech style guide for things like this. They use the format without a space, like BIP353. Briefly browsing the Bitcoin Dev Mailing List, I see all three formats used.

Personally, I prefer the space, but also happy top just follow OpTech. I really don't think it's a huge thing.