[WIP] csv_into (don't merge)

I like the `into` interface so much that I thought of this as a way to get stuff from disk:

```
df = csv_into(pd.DataFrame(), "data.csv")
bigdf = csv_into(pd.DataFrame(), "/path/to/csvs")
```
Error handling works like this:
```
df, errs = csv_into(pd.DataFrame(), "data.csv", permit_errors=True)
```
Errors are dropped and reported in `errs`
Right now this just leverages `pandas.read_csv`

TODO
- [ ] handle schemas via a `datashape` argument
- [ ] maybe support `sql_into`
- [ ] support URIs in the path argument