Add make builder DSL method
Update README and standardize docs
Output the contents of the RPM script, not the path

In the move from FPM to custom packagers, we made an incorrect
assumption that the scripts directive in the RPM spec file contained
the _path_ to the script, not the actual contents. This assumption has
proven to be faulty.

This commit changes the RPM packager and spec to output the contents of
the script file, not the path on disk.
Expose DSL methods in DEB packager for setting various configs
Expose DSL methods in RPM packager for setting various configs
Remove extra comment in PKG packager
Remove integration tests (we have harmony now)
Move Package::Metadata into its own class
Include Logging in Packagers
Do not cache the result of the Packager search
Do not require forwardable (it is not used)
Move directory helpers into Util module
Use the Metadata generator method in packager
Simplify packager step definitions
Cleanup packager base comments
Remove uses of Base#package_dir and use Config.package_dir
Remove uses of :execute and just use :shellout! directly
Cleanup packager base spec
Add primitive compressor classes
Add DMG compressor and specs