`respond_to?` predicate needs to be renamed

[Dmitry Gutov]

As discussed in #55, its current name overrides Object#respond_to? in an incompatible fashion.

We can rename it to responds_to?, for example. Just like includes? delegates to include?.

[Étienne Barrié]

The same issue exists with eql?.

h = {}
o = Object.new
def o.hash
  Dry::Logic::Predicates.hash
end
h[o] = true
h[Dry::Logic::Predicates]
# ! => lib/dry/logic/predicates.rb:181:in `eql?': wrong number of arguments (given 1, expected 2) (ArgumentError)