Remove get_ prefix from methods

Thanks to David Golden for the suggestion.
Always open filehandles as UTF-8

We're assuming that the data is in UTF-8, but for now that's a valid
assumption. YAML must be in UTF-8, and the file I/O stuff is probably
going away. (If it doesn't, I'll have to allow an 'encoding' parameter
or such.)
Text::FrontMatter::YAML 0.03