Log Message:
Update textproc/the_silver_searcher to 0.31.0.

pkgsrc changes:
o Switch MASTER_SITES to the author's site (in order to avoid the various
  auto* tools)

Changes:
o Add support for Crystal file types
o Add support for Racket file types
o Add support for Standard ML file types
o Add support for Elixir file type
o Misc bugfixes