Update all in-tree consumers of the BJson API to match. Also added
const-qualifiers to the BString versions of the API, and added the leading
"_" to the header guards.
As found on http://seriot.ch/parsing_json.php -- anything using the API
presently with valid JSON should have no troubles, but more valid JSON
that previously didn't work now does (e.g. JSON with root array nodes, not
root map nodes), and invalid JSON that silently succeeded before now fails.
Not all the bad cases from that testsuite now fail, and not all of the good
ones pass, but the few that remain are odd things that wouldn't map well to
the BMessage API (e.g. root string nodes, etc.) or are other behaviors that
make sense to leave as they are for compatibility reasons.
Based on an earlier piece of source code of mine that parsed JSON into
QObjects, this JSON parser creates a BMessage tree.
Will be used by Stephan in HaikuDepot for communication with the web app.
