Improve function typing

[Tygre]

Improve function typing by returning a value in an enum of RETURN_OK, RETURN_WARN, and RETURN_ERROR instead of an int. (See http://stackoverflow.com/a/742716)

[Tygre]

Unfortunately, C does not allow "strong" typing... I was thinking of defining

typedef enum {
    ERROR,
    WARN,
    OK
} return3_t

and have my functions return return3_t... but then C still allows comparison with any int because enumerated values convert into int!