garbage collected objects
proper lifetime management and sharing of object()'s

* allow a function to be mapped with some argument conversions being applied
  useful for binding to existing code and interfaces

* allow to specify whether a function is cold or not to use different optimization
  tag all constructors and destructors and register functions as cold for all functions
  (hot and cold)

* an not yet 100% complete example GD library binding, derived and supposed to be
  compatible with tcl.gd. Code size reduced to 10%, as the original was very boilerplaty.

* value (copy) semantics for objects, embedding in Tcl_Obj->internalRep for small types
* share callback objects between interpreters
* call object methods with dot notation (. $object method args) to avoid installing
  command handlers for each individual object