Add libkis: the Krita scripting wrapper library

libkis offers a QObject-introspectalbe wrapper around Krita's messy
internals. Some notes:

• Functions that return a pointer to a wrapper objectare factories:

the caller is responsible for deleting the wrapper object

• In principle, the library is meant to be low-level. Not a set of

macro commands, but an programming API

• Bindings in other languages are welcome
• Extensions are welcome.