Request - Add const modifier wherever possible in the mq2codebase.

[eqholic]

In the process of writing my first plugin in c++ I noticed that const is heavily underused in in the mq2 codebase. C++ strings only hand out const pointers to their internals and suddenly I have to write uggly stuff like this: WriteChatColor(const_cast<char*>(text), USERCOLOR_DEFAULT);
So please consider adding const wherever possible for more type safety and more options for the compiler to optimize.