Add Doxygen documentation for API changes from 1.6.0 to 1.6.1

Copied from my review board description:
This is a continuation of the API changes documentation started for describing
changes between releases. Most of the API changes were pretty simple needing
only to be brought to attention via the new "Asterisk API Changes" list.
However, if you see anything that needs further explanation feel free to
supplement what is there. The current method of documenting is to add (in the
header file): \version <ver number> <description of changes> and then to add
the function to the change list in doxyref.h on the AstAPIChanges page. I also
made sure all the functions that were newly added were tagged with \since
1.6.1. I think this is a good habit to start both for the historical aspect as
well as for the future ability to easily add a "New Asterisk API" page.

Review: http://reviewboard.digium.com/r/190/


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@180719 65c4cc65-6c06-0410-ace0-fbb531ad65f3

include/asterisk/utils.h

@@ -705,11 +705,13 @@ extern struct ast_eid g_eid;
 
 /*!
  * \brief Fill in an ast_eid with the default eid of this machine
+ * \since 1.6.1
  */
 void ast_set_default_eid(struct ast_eid *eid);
 
 /*!
  * /brief Convert an EID to a string
+ * \since 1.6.1
  */
 char *ast_eid_to_str(char *s, int maxlen, struct ast_eid *eid);
 
@@ -720,6 +722,7 @@ char *ast_eid_to_str(char *s, int maxlen, struct ast_eid *eid);
  *    00:11:22:33:44:55
  *
  * \return 0 success, non-zero failure
+ * \since 1.6.1
  */
 int ast_str_to_eid(struct ast_eid *eid, const char *s);
 
@@ -727,6 +730,7 @@ int ast_str_to_eid(struct ast_eid *eid, const char *s);
  * \brief Compare two EIDs
  *
  * \return 0 if the two are the same, non-zero otherwise
+ * \since 1.6.1
  */
 int ast_eid_cmp(const struct ast_eid *eid1, const struct ast_eid *eid2);