Add missing ampersands to filter lambdas in README.md

Fixed old typos in README.md

Add one more missing ampersand in README.md

Allow applying filters to any FilterSet

Since we want to apply filter expressions for dynamic segments, we need
to be able to apply filter expressions not just to Query#filters.

A Query can have a dynamic segment

A dynamic segment is a bit like a filter, except the subset happens
before dimensions and metrics are calculated.

This commits adds the ability to apply filter expressions, but for the
dynamic segment instead of the filters, mostly by reusing the existing
code for filter expressions.

Allow to define dynamic segment filters on Model

Dynamic segment uses filter expressions, just like plain filters.

This allows defining a dynamic segment in very much the same way filters
are defined.

Documentation for Dynamic segment