Upgrade httpclient

 - The old version was using ThreadLocals, which were never released
    causing memory leaks. The new version seems to be clean.
 - The offending class was
    `org.apache.http.impl.cookie.DateUtils$DateFormatHolder$1`
Upgrade parent pom

 - Also move htmlcleaner version to a property
Make 1.2 release

 Changelog:
  - Fixed memory leak in httpclient
  - Added better support for headers
  - General code cleanup, better docs and bugfixes
Start 1.3-SNAPSHOT development