fix path to data dir

when installed via pip, at least, regexes.yaml lives in 
.../lib/python2.7/site-packages/ua_parser-0.3.2-py2.7.egg/data,
but ROOT_DIR is .../lib/python2.7/site-packages/ua_parser-0.3.2-py2.7.egg/ua-parser.

this sets a DATA_DIR up top, and uses that, instead of ROOT_DIR,
to find regexes.{yaml,json}.