osx package should make available mruby-cli in user PATH

[toch]

cd #10 #17

[toch]

some resources that could be useful to build a osx package

• http://hogliux.github.io/bomutils/
• izpack.org
• http://stackoverflow.com/a/8016507/831180
• http://www.shivkaushal.co.uk/blog/2010/12/unpacking-an-osx-pkg-file/
• https://coolaj86.com/articles/how-to-unpackage-and-repackage-pkg-osx.html
• http://stackoverflow.com/a/11299907/831180