Initial commit of my ROT13 encoder app
Move functionality to javascript

Instead of reloading the whole page in a POST request on every submit
click, use javascript to retrieve the encrypted text and modify the
relevant page elements accordingly.
Use jinja2 filters to generate URLs for static content
Add 'load file' button

Add the function to load the text area from a file on disk.
Add 'clear' button

Clear the contents of the main input box on a single button click.
Add 'save' button

Let the user download the text area contents on button click.