Abstracted XML parser library and switched to autotools building.

expat is still the default parser, but libxml2 can also be used
via an option to the configure script.  New parsers can easily be
added by implementing a parser_foo.c that uses the interface defined
in parser.h.

tests/test.h

@@ -0,0 +1,16 @@
+#ifndef __LIBSTROPHE_TEST_H__
+#define __LIBSTROPHE_TEST_H__
+
+#define TEST_MAIN \
+    int main(int argc, char **argv) {\
+    int num_failed;\
+    Suite *s = parser_suite();\
+    SRunner *sr = srunner_create(s);\
+    srunner_run_all(sr, CK_NORMAL);\
+    num_failed = srunner_ntests_failed(sr);\
+    srunner_free(sr);\
+    return (num_failed == 0) ? EXIT_SUCCESS : EXIT_FAILURE;\
+    }\
+      
+
+#endif /* __LIBSTROPHE_TEST_H__ */