Dataclass support
#### Proposal  description

Dataclasses were added in Python 3.7.

It would be nice for pandas to support dataclasses. For example could be possible to construct dataframe from by calling `.from_dataclasses` or just `.DataFrame(data=dataclass_list)`. There should be also possibility to do `.to_dataclasses`.

#### Expected Behaviour

```python
from dataclasses import dataclass
import pandas as pd

@dataclass
class SimpleDataObject(object):
  field_a: int
  field_b: str

dataclass_object1 = SimpleDataObject(1, 'a')
dataclass_object2 = SimpleDataObject(2, 'b')
>>> asd

# Dataclasses to DataFrame
df = pd.from_dataclasses([dataclass_object1, dataclass_object2])
df.dtypes == ['field_a', 'field_b']
>>> True
df.dtypes == ['int', 'str']
>>> True

# Dataclasses to DataFrame
df = pd.DataFrame(data=[dataclass_object1, dataclass_object2])
df.dtypes == ['field_a', 'field_b']
>>> True
df.dtypes == ['int', 'str']
>>> True

# DataFrame to Dataclasses
df = pd.DataFrame(columns=['field_a', 'field_b'], data=[[1, 'a'], [2, 'b']])
dataclass_list = df.to_dataclasses()
dataclass_list == [dataclass_object1, dataclass_object2]
>>> True
```