[WIP] 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")
```


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I wanted to verify data validity from CSV->Blaze CSV OBJECT-> Blaze SQL Object.  Postgres interprets the date field correctly but I have to do a bit of munging to go from np.datetime64 to python datetime objects.  Perhaps the triple comparison is unnecessary?

In blaze, as soon as `SQL` is instantiated, the corresponding table is built in the DB. 

```python
In [1]: import psycopg2

In [2]: conn = psycopg2.connect("dbname=postgres host='localhost'")

In [3]: cursor = conn.cursor()

In [4]: cmd = """
SELECT table_schema,table_name
FROM information_schema.tables
WHERE table_schema = 'public';
"""

In [5]: cursor.execute(cmd)

In [6]: cursor.fetchall()
Out[6]: []

In [7]: from blaze import SQL

In [8]: url = 'postgresql://localhost/postgres'

In [9]: sql = SQL(url, 'foo', schema='{x: int, y: int, z: int}')

In [10]: cursor.execute(cmd)

In [11]: cursor.fetchall()
Out[11]: [('public', 'foo')]
```

But I do have some questions -- I started issue #467 to discuss them more fully