Dynamically use either inline_string escaping or uuencoding for extradata

Since luabins generates binary data which grows up to 3x by escaping,
it's more efficient to uuencode that instead.
A marker is placed as the first character of the value field, either
'e' for inline_string escaped text, or 'u' for uuencoded binary data.
The key is always inline_string escaped, as it will typically be
human readable.