Taint the RStrings, not the buffer

Was causing data corruption!
Merge pull request #4 from nevir/patch-1

Taint the RStrings, not the buffer
Support building gumbo as a packaged library via mini_portile, as the
default behavior. Use --use-system-libraries to install via system libs.
Switch up the package naming so you can just require 'gumbo' to get
all the goodies.
Support for greater tag inspection