The are going to be used to implement a kind of floating ref for liblinphone C objects.

optimize belle_sip_object_t (size field moved to vptr)
fix Makefile warning.

fix tester https_get_long_body to point to a more reliable address (I.E https://smtp.linphone.org/linphone.html)

Newer gcc forbids ";;"

Unit test updated for testing it.

Added a belle_sip_dict_t that has base accessors over this storage, and the appropriate unit tests.

Also, A resolution following SRV results now takes place in parallel.

 - Use size_t instead of unsigned int for offset.
 - Add function to enable marshal check at runtime.
 - Enable marshal check in unit tests.

 - Use our own implementation of snprintf() called belle_sip_snprintf() to handle the various native implementations whose return values are not consistent.
 - Simplify error handling in marshalling.

optimize to_string mechanism.

document object memory management.