A "public suffix" is a domain name under which Internet users can directly
register own names.

Browsers and other web clients can use it to
* avoid privacy-leaking "supercookies"
* avoid privacy-leaking "super domain" certificates
* domain highlighting parts of the domain in a user interface
* sorting domain lists by site

Libpsl:
* has built-in PSL data for fast access (DAWG/DAFSA reduces size from
180kB to ~32kB)
* allows to load PSL data from files
* checks if a given domain is a "public suffix"
* provides immediate cookie domain verification
* finds the longest public part of a given domain
* finds the shortest private part of a given domain
* works with international domains (UTF-8 and IDNA2008 Punycode)
* is thread-safe
* handles IDNA2008 UTS#46