Support Truetype instruction compilation

[jenskutilek]

Continuing from #335.

Main changes:

• Format of controlValue lib entry was not interpreted according to UFO spec
• Moved the instruction compilation from the post processor to the outline compiler
• Previous change allowed to remove the recompilation step of the whole font (https://github.com/googlefonts/ufo2ft/pull/335#discussion_r714668544)
• Don't write empty programs/tables to the font
• Always compile TrueType instructions if data is present (https://github.com/googlefonts/ufo2ft/pull/335#discussion_r714666011)

I also removed the separate additional UFOs from the test and implemented small tests for all methods of the InstructionCompiler as @anthrotype requested.

[anthrotype]

Thank you Jens. I hope to find the time too review this in the coming weeks, right now I am a bit busy with other things. Maybe you can ask @moyogo to take a look as well, if he's available.

[jenskutilek]

Thanks for letting me know. @moyogo, would you have time to take a look at my TrueType compiler code?

[moyogo]

LGTM! Sorry for the long delay.

[anthrotype]

Thanks Denis for reviewing this, however this is such a big change (1000 lines, 200 and more commits) and touches the core modules (the outlineCompiler) that I would like to also review this before it goes live.. I know it's been sitting here for months, but is there any particular reason you decided to merge now? I ask just to assess how urgent this is

[moyogo]

Ah, sorry I understood I was blocking this. What should we do?

[anthrotype]

What should we do?

revert, for the second time...

[jenskutilek]

I’ve made a new pull request with @moyogo’s and my changes , #654