#changes
Inline constant args for raptor_json_writer_literal_object

(raptor_json_writer_literal_object): Was always called with same
constants so inline them and update callers.
(raptor_json_writer_term): Added
Use raptor_json_writer_term() in several places

(raptor_json_serialize_statement): Use raptor_json_writer_term() for
s, p, o.

(raptor_json_serialize_avltree_visit): Use raptor_json_writer_term()
for final object.
Add len arg to raptor_json_writer_literal_object

(raptor_json_writer_literal_object): Remove use of
raptor_json_writer_quoted for constant string.
Add size arg to raptor_json_writer_blank_object

(raptor_json_writer_blank_object): use len and save a strlen

(raptor_json_writer_term): Update call to above
(raptor_json_writer_quoted): No need for strlen
(raptor_json_writer_literal_object): No need for strlen