2.2.0: Validation of database before deployment

• geoipupdate now verifies the MD5 of the new database before deploying it.
  If the database MD5 does not match the expected MD5, geoipupdate will
  exit with an error.
• The copy of base64.c and base64.h was switched to a version under GPL 2+
  to prevent a license conflict.
• The LICENSE file was added to the distribution.
• Several issues in the documentation were fixed.