Read documentation.html as webpage

pro-tip: use rawgit.com to read HTML
Won't handle getting slammed on HN though ;)
Merge pull request #202 from tomByrer/patch-1

Read documentation.html as webpage
[subset] Update maxp values when dropping hinting

Fixes https://github.com/behdad/fonttools/issues/201
[subset] If DSIG is to be retained, drop all signatures

Now DSIG can be retained by passing --drop-tables-=DSIG.
The embedded signatures will be dropped but empty table
retained.

Fixes https://github.com/behdad/fonttools/issues/145