Shoes console and manual should support system clipboard and save file

[IanTrudel]

The current implementation of Shoes console and manual does not provide advanced features that would be useful for real world usage, such as, copy to clipboard and save to file features. Select text with the mouse could be useful as well.

For example, a copy button and a save button to the left of run this button in the manual and left to clear button in the console.

[IanTrudel]

Shoes console implementation is likely to be straightforward:

• Need to fix issue System clipboard not working #13 to allow copy to system clipboard
• https://github.com/Shoes3/shoes/blob/master/lib/shoes/log.rb
  • Implement a copy button, save button
  • Both buttons will use Shoes.log to either copy to the system clipboard or to a file