Small doc fixes in bip-0360.mediawiki, noticed while implementing against the published vectors:
- The Test Vectors section linked P2MR_construction.json; the file on disk is lowercase p2mr_construction.json, so the link 404s.
- The same section still linked the rust implementation under bip-0360/ref-impl/rust, which #2202 moved out of the repository. Kept the python link and adjusted the sentence around it.
- The header said Version: 0.12.0 while the changelog's latest entry is 0.12.1.
- The 135-byte depth-1 witness example labeled the merkle path "(empty)" while counting 32 bytes for it. A depth-1 path has one 32-byte node.
Two things I left unchanged because they affect consumers' parsers: the schema mixes given.scriptTree (most vectors) with given.script_tree (the missing-tree error vectors), and a missing tree is encoded both as null and as an empty string. Happy to normalize those too if there is a preferred spelling.