"Simplify" overloading functions

[Nelson-numerical-software]

Currently, overloading is powerfull but not easy to manage.
To overload an operator, we need to manage many combination of types
example:
1 + 'c' requires to create double_plus_char function
A better (?) more compatible way could be to manage ONLY one type.

double_plus_char.m --> @double/plus.m

in plus.m we force types

function r = plus(a, b)
 A = double(a);
B = double(b);
r = A + B
end

• path search need to modified to search first overloaded functions
• do we consider overload of native types ? (example double overload or not ?)
  example: To allow to overload double can be "dangerous". It can break all existing code insidiously.
  It can also to be "slow" check each basic type will have a cost.
  Currently in Nelson, overload can "very" slow if overload is overloadbasictype(true)

overload with basic types could also have interesting use for code generation.
But we can also create special types to manage it.
example: 'Double'

• how to manage overloading with builtin (mex will be as functions)
  We can mangling function name for builtin: internal name could be @double/plus or @double:plus
  function will be never callable directly

• default behavior: What do we do if methods are not defined? Do we call default method ?

• reworks all existing overloaded functions to manage new overload algo

Test case: myComplex object with overload

@myComplex.zip

Why not directly move to classdef object in nelson ?
with this basic overload we can manage many cases.
classdef have advantage to have all overload method in same file but initial algo are same.
classdef will be considered later (certainly after v1.0)

[Nelson-numerical-software]

Need to be explored:
creates a function 'function t = toto(a)'
and an overload @int32/toto
and try to call 'toto(int32(9))'

[Nelson-numerical-software]

"first we need to have #491"
In fact, only define function_handle as a true type was enough (done)

[Nelson-numerical-software]

a poc was released and working. Need to be industrialized (in progress)

[Nelson-numerical-software]

In progress, on private branch

[Nelson-numerical-software]

A reminder about in progress

• add class type and use it
• add function_handle type
• reorganize types
• simplify validators module
• simplify operators
• vertcat
• horzcat
• isequal, ...
• sparse merge
• default class overload (as handle that already implemented)
• add overload level compatibility choice
• rework lookupFunction with new existing poc
• merging overloaded functions

[Nelson-numerical-software]

this feature took some time but it's just a first step.
LGTM