Modernized C Code

The current coding style of the Tk library is archaic, some examples/suggestions:

Note that these suggestions do not advice to rewrite the library, but I like to recommend to consider this for future code, or for reworked code. The disadvantage is that the library will contain two styles, the old and the new one. But I think this is better than to live with archaic code. And there exists powerful source code formatters which can be used to apply some of the rules to the whole library code.