Update of the titles highlighting

[eevan78]

I have noticed some recent changes to the syntax script for help files.
But the one I think is the most obvious for the vimhelp project is the change of the title highlighting.
So, the following:

vimhelp/vimhelp/vimh2h.py

Line 70 in c9bd7e8

PAT_TITLE = r"(Vim version [0-9.a-z]+|N?VIM REFERENCE.*)"

should become:

PAT_TITLE = r"(Vim version [0-9.a-z]+|N?VIM REFERENCE.*|N?VIM USER MANUAL.*|N?VIM - main help file)"