dup options
Switch to better error type
Force hash defaults to be either `nil` or `{}`
Name first parameter to method_missing
Fix specs
Allow wildcard hashes with `strip: false`
Use alternative exception syntax
Add a reader for options
Make Filter#filters and instance of Filters
Shorten HashFilter#default
Improve tests

-   Move common functionality into shared example group.
-   Name all contexts and examples.
Minor code cleanup
Improve documentation
Copy documentation from old filters
Add more documentation