Unify DEP spelling with a dash instead of a space (e.g. "DEP-0")

Replace all occurrences of DEP ([0-9]{1,2}) with DEP-N to ensure spelling is consistent with the DEP-0 spelling in the title of the original DEP-0 proposal.

Likewise, replace all occurrences of DEP([0-9]{1,2}) without a space with DEP-N with a dash.

Do not change filenames, but allow them to stay as depN or whatever.

This is aligned with the style of e.g. Ethereum Improvement Proposals (https://eips.ethereum.org/EIPS/eip-1).

Note all three alternatives:

• !13 (merged): DEP-0
• !14 (closed): DEP 0
• !15 (closed): DEP0

You can vote both up and down. You can also change your vote. Double votes will be manually nullified at final count as there is no technical way to prevent it.