Add Hash#deep_filter and Hash#deep_remove methods

[alexeymuranov]

Here are Hash#deep_filter, #deep_filter!, #deep_remove, and #deep_remove! methods for filtering deep hashes. This can be useful, for example, to filter params in a controller (this is how i am using it).

h = { :a => 1, :b => { :c => 2, :d => 3 }, :e => 4 }
kh = { :a => true, :b => { :c => true } }
h.deep_filter(kh)
# => { :a => 1, :b => { :c => 2 } }
h.deep_remove(kh)
# => { :b => { :d => 3 }, :e => 4 }

I am not sure about names. I was considering deep_only and deep_except, deep_keep and deep_remove, etc.

[alexeymuranov]

has_key? is for consistency with deep_remove!, where iteration is only over existing keys of key_hash.

[jeremyf]

All of the tests pass.

cc @tenderlove

[alexeymuranov]

Any thoughts about the names by the way? 'Filter' sounds too general, can be reserved for more complex operations. Maybe #deep_slice and #deep_except?

[rafaelfranca]

Hey guys. We think that this kind of things should go to plugins. Active Support is for things that we use in the Rails code and common patterns.

Thank you for the pull request.