scripts/; Added a README file and updated the keyword substitution scripts.

0.README:
  * New.  Provides a rational and quick setup steps for keyword substitution.

git_utils.py:
  * Updated FIX and ToDo comments.

git_keywords:
  * Speed hack: Check that an input line actually contains a $ before trying every keyword.
  * Code reformatting.
  * Added a FIX block with notes about suggested improvements to the code--which currently works, but could be even better.
  * Additional comments to help the reader.

../.gitattributes:
  * This file was not updated following the renaming of the 0.README in the repository root.  Fixed.

This code is good, and it works, but there is a bit of cruft hanging about and there are opportunities to make the code cleaner, clearer, faster, and more versatile.
Merge branch 'master' of github.com:ubiqx-org/Carnaval