Update the README.md
Implement the fixnum data type by tagged-pointer
Implement the character data type as tagged-pointer
Implement the boolean data type as tagged-pointer
Implement the empty list data type as a tagged-pointer
Change the type predicates for type boolean and empty list
Implement the eof object as a tagged-pointer
Implement the data type CLOSE_OBJECT, DOT_OBJECT and UNDEFINED as tagged-pointer.
Delete the unessential comments
Merge branch 'feature-tagged-pointer' into develop
Implement a trivial garbage collection seems like a garbage
Merge branch 'feature-ref-count' into develop
Remove the recursive calling when encounter CALL instruction

Store the current context at that moment, executes the new
instructions in compiled function, push the result and call the RETURN
instruction to restore the context.
Misc modification
backup
Merge branch 'feature-vm' into develop
Add the support for float-point number data type
Small size modifications
Decrease the duplication in source code
Small modification for refactoring