1.0.0 - Refactoring + New "double-flat" mode + API changes + documentation

API changes:

• Added support for a new "double-flat" mode so that users can create decorators creating signature-preserving function wrappers with zero level of nesting. Fixes #2.
• Generated var-positional name for kw-only methods is now '*_'
• can_first_arg_be_ambiguous parameter removed completely, it was too complex to use.
• callable_or_cls_firstarg_disambiguator renamed custom_disambiguator to be more intuitive
• wraps argument renamed flat_mode_decorated_name. It was too similar to the wording used in functools, and specific to the flat mode only. Fixes #1.

Improved behaviour

• Now the flat mode behaves exactly like nested mode concerning signature-related TypeError. This is because when you use the flat mode we now generate a nested mode function with a true signature.
• Now the exposed decorator uses the __wrapped__ trick to expose

Major refactoring for code readability:

• Submodules are now consistent and readable. In particular utils_disambiguation now provides a clear disambiguate_call method, and util_modes provides a clear make_decorator_spec to handle all the per-mode specificity and always come back to a nested case before going further.
• removed a case in the main module (var-positional) as it was completely covered by the general case.
• Information is now passed as objects through the various functions, using two main classes SignatureInfo (for static information) and DecoratorUsageInfo (for dynamic/usage information). The information is computed in a lazy way for each to avoid unnecessary signature binding for example.

Major documentation update.

See documentation page for details.