Refine bin/rubyscript

[judofyr]

Rename the current rubyscript to rubyscript-node.

Introduce a new rubyscript which works like this:

• rubyscript run test.rb -- Calls rubyscript-node test.rb
• rubyscript build test.rb --target v8 -- Builds a JavaScript version that can run on v8
• rubyscript build dir --target v8 --name Foo -- Builds a JavaScript library (a single file) containing all the Ruby files in the directory. You should be able to call Foo.run('test.rb') to invoke a specific file.
• rubyscript build dir --target b8 --name Foo --run test.rb -- Combines the two previous commands.