Opcode v1.2.0

Feature release: select and browse by source, and navigate directories.

- Search: a Source filter and a row of per-repository quick links, so any
  of the bundled sources (PayloadsAllTheThings, HackTricks, HTB-Scripts,
  Web-Security-Academy-Series, authored) is one click from all its
  content. Typing a source name now matches too, instead of returning
  nothing.
- Entry pages: an 'In this directory' section linking every sibling entry
  in the same source directory, so a directory README reaches each script
  beside it.
- References to HTB-Scripts and Web-Security-Academy-Series now point at
  GitLab (clone, attribution links, and the committed source_url values),
  matching where those repositories are developed.