Log Message:
Import serd-0.20.0 as textproc/serd.

Serd is a lightweight C library for RDF syntax which supports reading and
writing Turtle and NTriples.

Serd is not intended to be a swiss-army knife of RDF syntax, but rather is
suited to resource limited or performance critical applications (e.g. converting
many gigabytes of NTriples to Turtle), or situations where a simple
reader/writer with minimal dependencies is ideal (e.g. in LV2 implementations or
embedded applications).