Add new methods to set a value as a base64 encoded string of
a byte array. This uses the Rust base64 crate and encodes
directly into the JsonBuilder buffer with no intermediate
buffer required.
jb_set_base64: set a field on an object
jb_append_base64: append a value to an array
JsonBuilder is a Rust module for creating JSON output. Unlike
Jansson, the final JSON string is built up as items are added,
instead of building up an object tree and rendering it when
done.
The idea is to create a more efficient JSON serializer instead
of a flexible one.