Solve the programming task below in a Python markdown code block.
Implement `String#ipv4_address?`, which should return true if given object is an IPv4 address - four numbers (0-255) separated by dots.

It should only accept addresses in canonical representation, so no leading `0`s, spaces etc.
Also feel free to reuse/extend the following starter code:
```python
def ipv4_address(address):
```