Bump to version 0.2.1.dev.
Add methods to extract the version information from the browscap file.
Don't try matching against entries that don't have `:pattern` values.

We now create a `:browscap_version` entry to store the version
information from the browscap file. This is a sort of "virtual" entry
and isn't actually used for any sort of user agent string pattern
matching, only for internal version information.