#15 block & inline tag differentiation

[Derrick Oswald]

The tag-enders and end-tag-enders lists are only a
partial solution to the HTML specification for block
and inline tags. By marking each tag as a block or
inline tag and ensuring block tags don't overlap, a
better parsing job could be done, i.e.
<FORM> .... <TABLE> ...
</FORM></TABLE>

would be rearranged as
<FORM> .... <TABLE> ...
</TABLE></FORM>

This needs some design work.