Clamp functions does not work with int vectors

Functions such as `max`, `min` and `clamp` throw a TypeError when used with int vectors:
```
>>> glm.max(glm.ivec2(5), glm.ivec2(4))
Traceback (most recent call last):
  File "<input>", line 1, in <module>
TypeError: invalid argument type(s) for max()
```