Decopatch

Removed the clunky `Enum` for symbols. Back to a normal class, with a custom `__repr__`.

Now relying on `makefun>=1.5.0` where arg names changed a bit.

- We now provide predefined disambiguators `with_parenthesis` and `no_parenthesis`. Fixes [8](https://github.com/smarie/python-decopatch/issues/8).

- Fixed `KeyError` when the signature contains `**kwargs`. Fixes [9](https://github.com/smarie/python-decopatch/issues/9).

- Fixed issue when the signature only contains `**kwargs`. Fixes [10](https://github.com/smarie/python-decopatch/issues/10)

- Fixed static checker problem in PyCharm with the symbols (it came back when we moved to an Enum)

- Improved exception re-raising in flat mode.

- Minor: fixed init file.

Default-value symbols `DECORATED`, `WRAPPED`, `F_ARGS` and `F_KWARGS` now have a nicer representation. Fixes [7](https://github.com/smarie/python-decopatch/issues/7).

When a symbol is used in a signature where it can not be safely injected as keyword argument, an `InvalidSignatureError` is now raised. Fixes [6](https://github.com/smarie/python-decopatch/issues/6).

`makefun>=1.4.0` is now required, as it fixes a major issue: [5](https://github.com/smarie/python-decopatch/issues/5)

Default-value symbols `DECORATED`, `WRAPPED`, `F_ARGS` and `F_KWARGS` are now objects and not classes any more. This prevents IDE to flag the corresponding argument as being misused (not iterable...). Fixes [4](https://github.com/smarie/python-decopatch/issues/4).