Replaced FEVAL's with direct calls to function handles and removed support for old method of passing additional parameters.

Replaced instances of FEVAL for FFUN, GFUN, DGFUN, and EventsFUN with direct call of function handle. Removed support for passing optional parameters via additional arguments to main function (e.g., varargin in sde_euler()). Optional parameters must be passed, according to best Matlab practices, via the function handle itself. Processing of empty varargin's was costly.

FEVAL still used to handle RandFUN in case an overloaded function is passed. Unsure about this overloading issue - if it's needed or how important it is. FEVAl itself is not slow, just the extra varargin's.

Signed-off-by: Andrew D. Horchler <adh9@case.edu>