Remove old Q_ENUMS declaration
Remove old code from example4
Add vim_request_screen FIXME comment
Add functor callback argument to Neovim API calls

- For every API method there is now an additional public method
  in Neovim that takes an additional Functor argument - this
  allows you to pass a lambda as callback
- Added a unit test to the tst_neovimobject
- Due to symbol dependency, other files not need to include neovim.h
  explicitly, it is not enough to include neovimconnector.h
Fixed unittests

- All unit tests were broken in release builds - should be using
  QVERIFY instead of Q_ASSERT
- Removed deprecated test from tst_neovimobject