put PROTOTYPE-SPECIALIZER in separate ASDF system

Also separate implementation, tests and examples.
prevent delegation cycles in PROTOTYPE-SPECIALIZER
{EARLY,LATE}-PROTOTYPE-SPECIALIZER subclasses of PROTOTYPE-SPECIALIZER

* LATE-PROTOTYPE-SPECIALIZER is like the previous definition of
  PROTOTYPE-SPECIALIZER

* EARLY-PROTOTYPE-SPECIALIZER is used when a symbol naming a prototype
  object has to be turned into a specializer
mostly cosmetic improvements in PROTOTYPE-SPECIALIZER
make examples/prototype-specializer.lisp compilable
added test utilities {DEFINE,WITH}-SPECIALIZABLE-GENERIC-FUNCTION
initial tests for PROTOTYPE-SPECIALIZER
add PCL hot-patch with SPECIALIZER-TYPE-SPECIFIER

Suggested-by: Christophe Rhodes in #6

fixes #6
add arg-position to GENERALIZER-OF-USING-CLASS

* Adapt ACCEPT-SPECIALIZER, CONS-SPECIALIZER, PROTOTYPE-SPECIALIZER

Suggested-by: Christophe Rhodes in #3.

refs #2
add COMPUTE-EFFECTIVE-ARGUMENTS-FUNCTION

refs #2
add PCL hot-patch with MAKE-METHOD-LAMBDA-USING-SPECIALIZERS
add PCL hot-patch with MAKE-SPECIALIZER-FORM-USING-CLASS

* Includes "specializers name themselves" fix by Christophe Rhodes

* Use in PROTOTYPE-SPECIALIZER implementation

* Fixes use of EQL-specializers in PROTOTYPE-GENERIC-FUNCTIONs as
  witnessed by changes in test cases REMOVE-METHOD.SMOKE and
  CALL-METHOD.SMOKE
add COMPUTE-ARGUMENT-GENERALIZING-FUNCTION

fixes #2
optimization for COMPUTE-ARGUMENT-GENERALIZING-FUNCTION
refuse to load specializable system in non-SBCL and old SBCL