Added INSTALL file
Revert "Moved Xom to its own library libxom"

This reverts commit de2cb220d6abdedce91017f4bef86864fe822b14.

Conflicts:
	gxml/Makefile.am
	gxml/xom/Makefile.am
	test/Makefile.am
	test/SerializableTest.vala
Removed Xom last file.