New management of cf::operators

Operators are now defined in the cf::operators namespace.
Removing Named base class
New cf_scalar.h header file

The scalar types (Int, Float, Bool and Str) are not declared
in cf_scalar.h. cf_object.h declares only Object, NoneType and
UndefinedType.
Old code has been removed
Barton-Nackman trick for operators

All the binary operators (+, -, *, /, ==, !=, <, <=, >, >=) are
now member of the Object class; friend external template operators
are provided using the Barton Nackman trick.
cf_operators removed
hash_equal() removed
New header cf_internal_op.h
Sequence comparison operators
Mapping comparison operators
Hash now returns CPP representation

Hash representation uses now the CPP representation. Float scalar
representation displays all the available digits.
Method definitions from .h to .cpp
operators.md: computation with config object
++ and -- operators