Script to convert README.rst to README.html in application directory

You can now do:
```
make .htmls
```
in an application directory and README.rst will be converted to README.html based on the restructured text.  

It will also add a list of files to the README.html file for browsing through the important files in the directory.

This has been used to create the latest gallery, see for example
http://clawpack.github.io/doc/_static/geoclaw/examples/tsunami/chile2010/README.html

This has not yet been optimized, for example the Clawpack .css files are not used, so it's a plain white page, and the clawpack logo doesn't show up.