Whitespace cleanup
Stop prematurely escaping code block

Refactor Prism.highlight to HTML encode tokens before calling
Token.stringify.

This is a breaking change for nearly all grammars! Previously Prism was
encoding HTML entities *before* passing the code block to the parser.
Now it encodes HTML entities *after* the tokens have been parsed (before
rendering to HTML).
Attempt to fix clike and markup grammars

Original authors should at least verify these changes are correct