Idea: unite xlim and set_xlim to same function

I think it is confusing that the limits are normally set by `xlim` and in subplots by `set_xlim`.
Would it not be nice to use the same name  `ax.xlim(0,1)` for subplots ?

```python
import numpy as np
import matplotlib.pyplot as plt
plt.figure(1)
plt.xlim(0, 1)
plt.plot([1, 2])

fix, ax = plt.subplots()
ax.set_xlim(0, 1) ##  why not ax.xlim(0,1) ?
ax.plot([1, 2])
```