Rename unforbid to claim

[Penumbra69]

• closes dfhack #3183
• unforbid.lua -> claim.lua
• unforbid.rst -> claim.rst
• update documentation to use claim / claimed
• Update "forbid.lua" to hint at "claim all" instead of "unforbid all"
• added a note to the changelog.txt

[myk002]

the sphinx anchor has to be above a title. I think the verification script needs to be updated in this case.

The logic in this line would need to detect and skip over anchor definitions (lines starting with ..): https://github.com/DFHack/dfhack/blob/develop/ci/script-docs.py#L45

[Penumbra69]

I see now .. I haven't used Sphinx in a v. long time - I think I hive it sorted out this time.