Fix typo s/occurence/occurrence/.
get_last_request_uri: Replace crazy memset with char assignment.
Changed strnstr to strcmp wherever possible in response to ticket #30.

Thanks MrNex.

Altered by me:
* Updated to use strstartswith instead of strncmp.
* Cleaned up xp_parser.c with whitespace cleanups.
* Added very basic xp_parser testcase.
* Fixed spelling of occurrence (again).
* Added missing strstartswith (doctype).
* Properly seek past xml prelude.

Closes #30.
Improve get_peer_tag. Improve SIP parser a bit.
tests: Move tests into the respective source files whenever possible.