Add ReST markup module.

It support basic translation such as `function' to ``function``.
Add ReST block marker to indented text.
Mark lisp block with code ReST keyword.
Print help message if -h or --help argument given.
Print error message if can't find Cask file in cwd.
Move read_cask_file to cask module.
Add README.rst template example.
Add read_package_file function.