tests: rename s/tests/test/ for consistency

Signed-off-by: David Aguilar <davvid@gmail.com>
jsonpickle: docstrings tweaks

Signed-off-by: David Aguilar <davvid@gmail.com>
jsonpickle: add convenient dumps() and loads() aliases

Signed-off-by: David Aguilar <davvid@gmail.com>
backend: return a success bool from load_backend()

Return True when load_backend() succeeds.  Simplify JSONBackend by
moving common arguments into load_standard_backend().

Signed-off-by: David Aguilar <davvid@gmail.com>