Support packaging additional files

[jacob-carlborg]

It would be nice if Pkgr supported packaging additional files that are not located in the specified directory/tarball. Ideally both in the .pkgr.yml and as a command line flag. Something like:

# .pkgr.yml
directories:
  source1: target1
  source2: target2

Currently I have a need to add some additional files and I currently do that by copying them the the project directory with an after compile/build script. Then I have an after install script that moves the files to the correct location.

Fpm supports this by specifying arguments with no flags on the command line. = can be used to separate source from target path, i.e. fpm -s dir -t rpm foo source1=target1 source2=target2.