Release 2.3.0

• Major revamp of all type-related functionality: each type is now represented by a type tag/symbol; procedure type-for from library (lispkit type) can be used to determine the type tag of a given object; breaking change for make-type, which now returns 5 values (the first is a new type tag)
• Support complex numbers for trigonometric and inverse trigonometric functions in library (lispkit math): sin, cos, tan, asin, acos, and atan
• Bug fixes in library (lispkit draw chart bar) and (lispkit enum)
• New library: (lispkit math matrix)