#5067 htmldoc 1.8.30 with Xcode9 fix

[Hanspeter Niederstrasser]

Updates to latest 1.8 release (v1.9.1 is latest upstream).
This release has fixes for our existing patch
https://github.com/michaelrsweet/htmldoc/issues/282
https://github.com/michaelrsweet/htmldoc/issues/291

I added the upstream fix for the pointer <--> zero comparison, which is in v1.9
https://github.com/michaelrsweet/htmldoc/issues/306

I stayed in the 1.8 series to be conservative.

[Daniel Macks]

thanks!