Merge: Inkscape tool revamp and gamnit support

* Clean up old style inits, add missing doc and refactor main code into classes and methods.
* Adds the gamnit target option, the generated code is much more simple, but the generation a bit more complex.
* Allow to specify the full path to the Nit source file to generate.
* Make rounding to the next power of 2 optional, it will no more be required for mnit programs on Android with #1284.

Pull-Request: #1285
Reviewed-by: Jean Privat <jean@pryen.org>
Reviewed-by: Alexandre Terrasa <alexandre@moz-code.org>