#5 Add IN, OUT and INOUT function argumets descriptors

[Mihail Churbanov]

Currently in/out arguments are described in comments before functions.
Defining IN, OUT and INOUT can improve understanding of arguments in some functions without searching it in source code - they could be shown in IDE help popup messages. For example:
...
#define IN
#define OUT
...
void cvarSomeFuntion(int IN somevar, double * OUT result)
...