Cleanup keyboard code

[drmfinlay]

This PR cleans up the keyboard code a little and fixes some bugs.

Summary:

• Change the Key and Text action classes to calculate keyboard
  events at execution time instead of initialization time.
• Fix a regression with keyboard input actions on Windows.
  This restores the list of extended keys removed from sendinput.py in PR 343. If the specified virtual-key is in this list, e.g. the insert key, then the KEYEVENTF_EXTENDEDKEY flag is used.
• Fix a bug with Text action default pause values.
  This change fixes a bug where the PAUSE_DEFAULT setting in the Windows-only settings.cfg file is not used properly by Text actions.
• Fix numerous code style issues.
• Remove doc build conditionals from keyboard/init.py.
  These should be removed from other files too. I plan to do that as part of a more general clean up of the platform code.

[LexiconCode]

Let me know when this is ready to test!

[drmfinlay]

Should be ready to test now. I can already see a problem with Key("") that I'll fix shortly.

I'd like to merge 326 before this; I anticipate a fair few conflicts.

[LexiconCode]

In my limited testing this does fix #350

Is this PR meant to address the difference in speed between DNS text output versus dragonfly?

[drmfinlay]

Yes. It looks like that problem is caused by incorrect pauses in the Typeable event methods. I think it is still not quite right. It would not have been helped by the bug I fixed with aaff1ba.

[LexiconCode]

Yes. It looks like that problem is caused by incorrect pauses in the Typeable event methods. I think it is still not quite right. It would not have been helped by the bug I fixed with aaff1ba.

We are all human! At least I hope :) Let me know if you can hear a high-pitched squeal from one of my fans going bad as you read this text.

[drmfinlay]

Haha :)

Well, I can confirm that the behaviour doesn't occur for me using the hardware or Unicode events. It is the same speed as DNS if I set pause_default to 0.

Incidentally, I plan to remove the settings.cfg file in the future; the settings are either defunct or better handled by setting class/instance members instead.