Deprecation howto

Sometimes code has to be removed. This is how you do it without you inform other.

1. In the header file wrap the method signature into the OF_DEPRECATED_MSG("message", signature)-makro. You should also hint at any replacement functions, e.g.

   OF_DEPRECATED_MSG("ofxFoo::initFoo(int bar) is deprecated, use foo(int bar) instead.", void ofxFoo::initFoo(int bar));

2. Remove the actual implementation code.

3. Add the "@deprecated" tag to the Doxygen documentation.