Allow querying/filtering of custom classes

This release fixes #14. You can now query/select/filter data with custom classes.

Documentation improved, better avg function

This release improves the avg() function to return a normal number. To do that I had to fix the reduce() function to always add the index and array parameters to each reducer function call.
This release adds tests for the documented replacer/reviver functions.
The manual now explains how to extend JAQT.

Stable API (groupBy and reduce)

This release includes a refactored groupBy function, a reduce function and an improved _ function. Read the updated documentation for the specifics. This release edges closer to the dreaded 1.0, hopefully the API will not need any more changes before than.

Getting to stable

This release is close to complete and stable. You can filter and select from Arrays or Objects. The from() proxy will allow chaining even on empty result sets. The select syntax has almost reached feature parity with GraphQL, and adds all the features of javascript on top.