include soup.h in header file

We use soup symbols in gstdlnasrc.h (SoupSession and SoupMessage); header
files shouldn't rely on extra headers being already included.
move NPT parsing code to util.c

This will allow this function to be properly tested as it's not static any
more.
add src/Makefile.am

Much cleaner to have its proper Makefile.
add tests infrastructure
dlna_src_parse_npt_range: start by initializing output variables

If the function is supposed to free the ouput variables, it should always do
it, even in case of failure, to avoid leaks.
add tests for do_test_parse_ntp_range()
Merge pull request #134 from gdesmott/tests

Add tests infrastructure