Can `stdlib_list(version)` default to the current version?

I think it would be convenient if this would work (on a python 2.7 installation):

```
from stdlib_list import stdlib_list
stdlib_list() == stdlib_list("2.7")
```

ie. that the version parameter defaults to the Python version you're running on, since creating that parameter is tedious and non-obvious:

```
stdlib_list('.'.join(str(x) for x in sys.version_info[:2]))
```
