[MERGE] Add a brief Portability section to HACKING, build HACKING.htm from 'make docs'.

[Martin Pool]

Martin Pool has voted +1.
Status is now: Approved
Comment:
You could add the generated HACKING into index.html too...

For details, see: 
http://bundlebuggy.aaronbentley.com/request/%3C20070412054524.GF6345%40steerpike.home.puzzling.org%3E