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This reverts commit 626ab4d0.

Lacked http sources
Handle moved grammars sources

add possibility to force rtpmap for static payload types at compilation time using macro BELLE_SDP_FORCE_RTP_MAP

 - 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.