Feature/csv to sql natively

When finished, this PR should address #352. New `into` function calls out to to native COPY function of various DBs.  Has optional `if_exists` argument (similar to pandas) to handle three cases: replace, append, and fail

```python
into(sql,csv, if_exists="replace")
```

This PR currently handles the native copy calls for:

- PostgreSQL
- MySQL
- SQLITE


- [x] Travis CI PostgreSQL Testing
- [ ] Travis CI MySQL Testing

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I'm not sure, actually. I checked out https://github.com/quasiben/blaze/commit/ef1b07a8044f80772b6b330ac3e0d608d80ec433 and re-ran; all the CSV data descriptors had correctly supplied `csv.header` as `False`.