src/lahocorasick: Check that search is given a callback
rockspec: Bump version

  - Update external_dependencies to use MULTIFAST
  - Remove citation from summary
src/lahocorasick: Update to Multifast 1.4.2

  - New function signature for init(), callback is given to search() directly
  - Throw errors when search fails
  - Search return if callback broke loop
src/lahocorasick: Add `keep` argument to search