Ensure graceful handling of UTF-8 characters

Forcing the encoding to UTF-8 ensures that vim, when started in a
non-UTF-8 environment, can gracefully handle the presence of UTF-8
characters in the file. Instead of generating errors, extended
characters will be transliterated.
Merge pull request #28 from elliterate/handle_utf8_chars

Ensure graceful handling of UTF-8 characters