Export `query()` function

[cowboyd]

The underlying api for map, filter, reduce and friends is actually useful in its own right if you want to start your own queries from a base iterable, so that instead of:

for (let desc of map(state.todos, todo => todo.description)) {
}

You can say:

for (let desc of query(state.todos).map(todo => todo.description) {
}

It's more than just stylistic though since queries are monadic, you can make them arbitrarily complex.