Add support for generated constants in RPG:: classes

[mateofio]

Towards fixing EasyRPG/Player#1516

Also adds panning constants, so that the default pan values don't need to be duplicated between player and liblcf.

[carstene1ns]

Thanks! This will also be very useful for #245.

[Ghabry]

Lets make a quick style discussion:
I find Hungarian notation really ugly. Is that some common idiom in C++11 code to prefix constexpr-constants with a German "konstant"-k?

[mateofio]

From my understanding, hungarian notation is where you add a prefix or suffix to say the type. And that to me is horrible. Its useless info and when you change the type you have to change the name too. I hate it.

Using "k" constant is not a C++11 thing. It just a style habit I picked up. It's not because it's german, it's because kSomeConstant stands out more readily than cSomeConstant. Similar to using "e" for eEnumValue.

I don't much care what convention we use. We just have to pick one.

[Ghabry]

Ah I thought it is k because c is the prefix for classes.

I dislike using e for enum but for the k we did a quick poll and the result is:

We don't kare

[mateofio]

Fixed the whitespace. I also redefined the panning constants as X * 256