Parse and process snapshot, remember RRDP URIs (session ID and serial).

Parse and process snapshot, remember RRDP URIs (session ID and serial).

+Create struct and method to store RRDP URIs data.
+Create handler so that multiple threads can access RRDP URIs data.
+Rename 'gdata' property to 'global_data' at update_notification struct.
+Use prefered access method according to the order specified at the CAs.
+Implement RRDP URIs comparison, considers: URI, session ID and serial so that the caller can determine what to do (process snapshot, deltas, etc.)
+Document rrdp_objects.h structs.
+Add content length to 'publish' structure.
+Add functions to parse 'publish' elements.
+Validate that a new RRDP object parsed matches session ID and serial of the parent.
+Whenever a snapshot file is parsed (and validated), all of its 'publish' elements are parsed as well and created at the local repository.
+Use 'fnstack' to log whenever an RRDP file is being processed.
+Update 'uri.h' to explicitly create either rsync or https URIs.
+Use rrdp_handler at the validation state of each thread (or each TAL, it's the same thing).
+Fix wrong return value on error at __do_file_validation, it should return a 'no memory' error instead of 'invalid value'.
+Fix macro ARRAYLIST_FOREACH, one argument wasn't being utilized.
+Update unit tests, add reference to new header 'db_rrdp.h'.