Support `Any` as an alias for `object` to describe a default typeclass implementation

**Context.** In order to define a default implementation (the one used if no other implementation matches), we currently have to write something like this:

```python
from classes import typeclass

@typeclass
def render(data_value) -> str:
"""Render a data value nicely."""

@render.instance(int)
def _render_int(data_value: int) -> str:
return f'This is an integer: {data_value}'

@render.instance(object)
def _render_int(data_value: object) -> str:
return f'No idea what this is: {data_value}'

assert render('BADOOM') == 'No idea what this is: BADOOM'
```
*(this script should be runnable as-is.)*

**Decision.** Support `Any` as a special case to replace `object`:

```python
@render.instance(Any)
def _render_int(data_value: Any) -> str: # type: ignore
return f'No idea what this is: {data_value}'
```

**Consequences.**
* Pro: The code will look a little bit more straightforward;
* Contra: `mypy` with common settings might be unhappy about `Any` being used, but that can be silenced with `type: ignore` I suppose.