Fixed bad relative URLs in v4 of XHTML 1.0 Frameset DTD
Fixed bad relative URLs in v3 of XHTML 1.0 Frameset DTD
Fixed relative URLs in XHTML Frameset DTD for older versions
Fixes #53. Rearranged XHTML 1.1 DTD in order to correctly register th:block
Fixed version number in v4 DTDs
Fixed version number in v3 DTDs