Better code blocks for examples.

[bufferhe4d]

Changing the example code to minted instead of lstlistings. This results in code blocks that are easier to copy and paste and have better syntax highlighting. We lose the line numbering in the code blocks but there aren't many instances where the documentation refers to specific line numbers.

README has also been updated with the new build instructions (since minted requires the -shell-escape flag while building the dtx).