clang-format config

[PROP65]

clang-format does not have the most granular configuration so some things (like different pointer placement on unnamed arguments in function prototypes) are not currently achievable.

From the tinkering I've done with it so far it seems that formatting before building yields better results. If formatting is done on the final header file all preprocessor directives will be further indented.

Major changes compared to current styling:

• preprocessor directive indentation
• max line length of 160

I'm open to changing the current config if needed, I'll admit it's far from perfect.

If needed I can format the src folder and rebuild once the style config is agreed on.

Here's nuklear.h after formatting and rebuilding with this change
https://gist.github.com/PROP65/bf35c5a22a210584d5057fb2b6a1323d

[PROP65]

#739