Pass header & events as null-terminated strings

[Youka]

ASS is a text format, there will be no null character in header or event, so outsourcing character counting is just pushing work to users.

[torque]

As I stated in my comments on #5, I don't have a problem with adding an alternative api function that lets the user provide events as a string. But I also don't see a good reason to get rid of the current api function.

edit: in concert with #7, the current assi_addEvent method could be changed to assi_pushEvent

[Youka]

The functions with characters counting could just end with _str and call their variable length equivalents with the length parameter calculated by strlen on data - that simple. Though i would prefer they replace the old (->their names) which get _n appended, following the usual C style.

[torque]

I don't see a good reason to start appending things on the end of function names, usual C style or not.

I'd like to avoid using _ in identifiers as much as possible. It's useful for visually separating the namespace from the function name, but other than that, it should be perfectly easy to create descriptive function names without needing to append garbled characters to the end.

for example, something like:

int assi_addEventsFromString( const char *eventString );
// Following two functions are interchangeable. If `eventLength == 0`, use
// `strlen` to determine length.
int assi_pushEvent( const char *event );
int assi_pushEventWithLength( const char *event, const unsigned int eventLength );