Adding recipe for rtags, c/c++ tags package

- Requires clang to be installed on the computer
- Requires the user to be running a specific daemon
  which is built with the :build() commands provided
  in the recipe
Merge pull request #1776 from LefterisJP/master

Adding recipe for rtags, c/c++ tags package
http callback: don't write-file directly to dest

When downloading a .gz file, if we actually write-file to that filename
the compressed data would be compressed a second time thanks to
auto-compress-mode. Instead, write to .part file first and then rename
to the destination, as it was before
92a39c84febd19bf0d83f7b442726051f0809a9e.