allow using Iterable in Series and DataFrame constructor
- [X] closes #2193
- [x] tests added / passed
- [X] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry
---

@TomAugspurger Hope you can review this.

BTW, perhpas you may want to change `Iterable` in `is_list_like()` to `Sequence`.

```python
gen = (i for i in range(10))
pandas.core.dtypes.inference.is_list_like(gen)
# True
len(gen)
# Traceback (most recent call last):
#   File "<stdin>", line 1, in <module>
# TypeError: object of type 'generator' has no len()
gen[0]
# Traceback (most recent call last):
#   File "<stdin>", line 1, in <module>
# TypeError: 'generator' object is not subscriptable
```
