srd_inst_new() used the decoder ID as the instance ID, preventing the use
of multiple instances of the same decoder in the same session. Simply
append a numerical suffix to later instances to allow more.
Required changes to cleanup to reliably free all memory. Valgrind checked.
This fixes parts of bug #868.
Based on original work by: Soeren Apel <redacted> Signed-off-by: Karl Palsson <redacted>