Add ability to add to Rakefile without specifying a bunch of lines in .sync.yml

[ghoneycutt]

Adding lines to the Rakefile in .sync.yml is not ideal as you must turn readable ruby code that can be parsed and linted into an array of lines in yaml. Instead we should allow users to have a Rakefile.local

[ghoneycutt]

I'm currently doing this with adding this to a .sync.yml

Rakefile:
  extras:
    - "if File.readable?('Rakefile.local') then load 'Rakefile.local' end"

[ghoneycutt]

PR #218 would make this default behavior.

[rodjek]

Rake has the built in ability to load tasks from external files and I'd prefer to suggest people use this instead. If you create a rakelib directory at the root of your module, rake will automatically load any *.rake files in that directory, allowing you to specify and custom tasks that you wish without modifying the Rakefile itself.

[ghoneycutt]

Thanks @rodjek

That worked great and I've updated the PR to document this.