Support for Extraction Filter

[sid88in]

http://druid.io/docs/latest/querying/filters.html

{
"filter": {
"type": "extraction",
"dimension": "product",
"value": "bar_1",
"extractionFn": {
"type": "lookup",
"lookup": {
"type": "map",
"map": {
"product_1": "bar_1",
"product_5": "bar_1",
"product_3": "bar_1"
}
}
}
}
}

[dakra]

Extractions are in pydruid.utils.dimensions.
Map lookup extraction in particular is defined here: https://github.com/druid-io/pydruid/blob/master/pydruid/utils/dimensions.py#L123

[magor]

@dakra , could you please elaborate on how to use linked class in filter specification (as in, using pydruid.utils.filters.Filter class)?

This pull request seems related: #76

[dakra]

@magor I was thinking about dimension extractions. You're right that for lookup extraction on the Filter you have to wait for #76