Make valid? work with Unicode and punycode domains

clean converts Unicode domains to punycode, but PublicSuffix does not
have punycode versions of the Unicode TLDs.

Therefore, convert back to Unicode before checking valid suffix.
Merge pull request #11 from swiftype/master

Make PostRank::URI.valid? work with punycode and Unicode domain names
Remove PHP session id parameter when canonicalizing URLs
Merge pull request #12 from swiftype/remove-phpsessid

Remove PHP session id parameter when canonicalizing URLs
Don't unescape `+` in url path; fixes #14
Merge pull request #15 from coreyward/master

Don't unescape `+` symbols in URL path
Merge branch 'master' of github.com:postrank-labs/postrank-uri