Prevent regex intensive execution which may cause DoS

[giosh94mhz]

There are many dot-asterisk greedy matches which may cause
very intensive, even indefinite, execution of the script.

The worst one was the schemeRe match, which if executed
(by accident, or by honoring the MIME headers) against a
base64 text will cause infinite execution.

This patch tested against a ~1MB file, will drop execution
wall-clock time from many hundred of seconds, to a couple of seconds.

[giosh94mhz]

The limit on the scheme to 16 chars, has been set checking against the list in issue #4 , and 16 looks ok to me.

Increasing this number to let's say 32, will slow down my samples from ~1 seconds to ~5 seconds, but still better then keeping an open match.