CSP browser client defaults to utf8 encoding

All the CSP server stuff defaults to _utf8_ encoding - this seems to be the
only instance defaulting to _plain_. Avoids issue trying to decode on server
when input is not encoded.

Resolves #63. However, it is recommended that `std.utf8.decode` does not mix
deprecated `escape`/`unescape` with `encodeURIComponent`/`decodeURIComponent`.