Improve PrettyPrinter construction perf by not using uniqid

The uniqid function is *very* slow on unix systems. The code has no
particular unique-ness requirements, so the much faster mt_rand()
function is used instead.

Closes PR #65.
Fix pretty printing of `include` expressions
Fix notices when generating expected tokens list
Fix notices when generating expected tokens list (continued)

Forgot to add regenerated parser
Remove obsolete item from grammar/README.md
Add PHP 5.5 to .travis.yml