Miscellaneous tweaks to the README.

For legibility, and (most of all) fidelity on GitHub; also aligned some description
with the blog post.
Fix the screencast link. (fixes #16)

It used to point to my personal upload of the screencast, since taken down;
now it points to Inkling's upload.
Remove the UIAElement macros from the example test case.

They are not strictly required, but are merely debugging aids.
The example is simpler without them, and the FAQ describes their use
(and gives an example).
Convert all code blocks to the "fenced" style.

So that GitHub will color them according to their language's syntax.