Added missing docblocks.
Changed str() function name to native() as it is more descriptive about what the function does.
Fixed a typo.
Added the native() function to all primitives.
Fixed the native() functions declaration.
Moved the native() functions to the PrimitiveX classes.
Added tests for the native() functions of all primitives.
Allow only native values for the object's value. This fix prevents a cyclic declaration, where the Primitive could contain a Primitive object as a value.
Changed the functions to profit from the native() functions.