WIP: Regex and Like expressions

closes #567 

TODO:

- [ ] SQL
- [ ] MongoDB
- [ ] streaming Python
- [ ] `bcolz`?
- [ ] `numpy`?

`Regex` example:

```
In [4]: df
Out[4]:
    name sex  amount  id
0  Alice   F     100   1
1  Alice   F     100   3
2   Drew   F     100   4
3   Drew   M     100   5
4   Drew   M     200   5
5    Bob   M     500   6
6    Bob   M     300   7

In [5]: from blaze import TableSymbol

In [6]: from blaze import discover

In [7]: t = TableSymbol('t', discover(df))

In [8]: t
Out[8]: t

In [9]: t.schema
Out[9]: dshape("{ name : string, sex : string, amount : int64, id : int64 }")

In [10]: expr = t[t.name.regex('(?:A|B).*')] # get alice and bob

In [11]: expr
Out[11]: t[Regex(child=t['name'], pattern='(?:A|B).*')]

In [12]: from blaze import compute

In [13]: result = compute(expr, df)

In [14]: result
Out[14]:
    name sex  amount  id
0  Alice   F     100   1
1  Alice   F     100   3
5    Bob   M     500   6
6    Bob   M     300   7
```