Allow disabling of more features

[bagder]

This is a patch set that

1. Makes the #ifdefs for features disable more code that isn't used
2. Adds more defines to disable more specific features if desired (not all yet available via easy configure options)
3. Adjusts tool code to be able to run with a libcurl built with features disabled
4. The API/ABI is maintained but will return errors for disabled features.

[bagder]

Blah, silly me. It broke because it relies on something like #3846 so I'll get that fixed and landed first, then fixup this branch again and push a fix.

[bagder]

I'm having a hard time figuring out why the windows CI builds fail like this, so I'm more or less bisecting in the separate branch bagder/ci. I might then land some of the commits piecemeal instead once proven to pass the CI.

[MarcelRaad]

Ah, here is the PR I was looking for. Did you forget a "Closes" line? These are in master now and broke the HTTP-only AppVeyor tests.

[bagder]

Only some of them are in master, the ones I (wrongly apparently) thought didn't break master...