Regex dispatcher for `resource`

We might want to break up the resource function which converts URI's into data objects of some form or another.  We can't use our normal dispatching tricks here because we can't dispatch on type.  

Instead lets dispatch on regular expressions
```Python
    >>> f = RegexDispatcher('f')

    >>> f.register('\d*')
    ... def parse_int(s):
    ...     return int(s)

    >>> f.register('\d*\.\d*')
    ... def parse_float(s):
    ...     return float(s)

    Set priorities to break ties between multiple matches.
    Default priority is set to 10

    >>> f.register('\w*', priority=9)
    ... def parse_str(s):
    ...     return s

    >>> f('123')
    123

    >>> f('123.456')
    123.456
```

We use this to register datatypes, e.g.

```Python
@resource.register('(sqlite|postgresql|mysql)://.*')
def resource_sql(uri, table_name, *args, **kwargs):
    return SQL(uri, table_name, *args, **kwargs)
```

This lets us call things like

```Python
>>> resource('/path/to/file.csv')
<csv object>

>>> resource('sqlite:///my.db::table_name')
<sql object>
```

We plug this into the interactive `Table` object

```Python
In [2]: Table('examples/data/iris.csv')
Out[2]: 
    sepal_length  sepal_width  petal_length  petal_width      species
0            5.1          3.5           1.4          0.2  Iris-setosa
1            4.9          3.0           1.4          0.2  Iris-setosa
2            4.7          3.2           1.3          0.2  Iris-setosa

In [5]: Table('sqlite:///examples/data/iris.db::iris')
Out[5]: 
    sepal_length  sepal_width  petal_length  petal_width      species
0            5.1          3.5           1.4          0.2  Iris-setosa
1            4.9          3.0           1.4          0.2  Iris-setosa
2            4.7          3.2           1.3          0.2  Iris-setosa

# Set up Blaze server elsewhere
In [7]: from blaze.server.client import *
In [8]: Table('blaze://localhost:5000::iris')
Out[8]: 
    sepal_length  sepal_width  petal_length  petal_width      species
0            5.1          3.5           1.4          0.2  Iris-setosa
1            4.9          3.0           1.4          0.2  Iris-setosa
2            4.7          3.2           1.3          0.2  Iris-setosa
3            4.6          3.1           1.5          0.2  Iris-setosa
```
cc @talumbau