A multimethod to convert a backend RDF literal into a corresponding
Clojure type.  This method can be extended to provide custom
conversions. You should typically not need to call this directly,
instead see backend-quad->grafter-quad.

Convert an RDF4j backend quad into a grafter Quad.

A default set of common prefixes

Convert a grafter IStatement into a backend (RDF4j) statement type.

Coerces destination into an java.io.Writer using
clojure.java.io/writer and returns an RDFWriter.

Use this to capture the intention to write to a location in a
specific RDF format, e.g.

(grafter-2.rdf/add (rdf-writer "/tmp/foo.nt" :format :nt) quads)

Accepts also the following optional options:

- :append        If set to true it will append new values to the end of
                 the file destination (default: `false`).

- :format        If a String or a File are provided the format parameter
                 can be optional (in which case it will be infered from
                 the file extension).  This should be a clojure keyword
                 representing the format extension e.g. :nt.

- :encoding      The character encoding to be used (default: UTF-8)

- :prefixes      A map of RDF prefix names to URI prefixes.

Attempts to coerce an arbitrary source of RDF statements into a
sequence of grafter Statements, using the RDF4j backend.

If the source is a quad store quads from all the named graphs will
be returned.  Any triples in an unnamed graph will be ignored.

Takes optional parameters which may be used depending on the
context e.g. specifiying the format of the source triples.

The `:format` option is supplied by the wrapping function and may be
nil, or act as an indicator about the format of the triples to read.
Implementers can choose whether or not to ignore or require the
format parameter.

The `:buffer-size` option can be used to configure the buffer size
at which statements are parsed from an RDF stream.  Its default
value of 32 was found to work well in practice, and also aligns with
chunk size of Clojure's lazy sequences.

The `:base-uri` option can be supplied to automatically re`@base`
URI's on a new prefix when reading.