This patch adds initial support for decoding/encoding to/from the new
maps data type.

I'd like to thank Jihyun Yu (yjh0502) for the initial versions of this
work.

By default Jiffy is quite strict in what it encodes. By default it will
not allow invalid UTF-8 to be produced. This can cause issues when
attempting to encode JSON that was decoded by other libraries as UTF-8
semantics are not uniformly enforced.

This patch adds an option 'force_utf8' to the encoder. If encoding hits
an error for an invalid string it will forcefully mutate the object to
contain only valid UTF-8 and return the resulting encoded JSON.

For the most part this means it will strip any garbage data from
binaries replacing it replacement codepoint U+FFFD. Although, it will
also try and the common error of encoding surrogate pairs as three-byte
sequences and reencode them into UTF-8 properly.