dry-types 1.3.0 on Ruby Gems

Schema#merge for merging two hash schemas (@waiting-for-dev)
Aliases for .constructor to non-constructor types. Now you can call .prepend/.append without silly checks for the type being a constructor (flash-gordon)
```
(Dry::Types['integer'].prepend(-> { _1 + 1 })).(1) # => 2
(Dry::Types['coercible.integer']  >> -> { _1 * 2 }).('99') # => 198
```
Hash::Schema#clear returns a schema with the same options but without keys
Optional namespace now includes strict types by default (@flash-gordon)

Schema::Key#optional returns an instance of Schema::Key as it should have done
Composition with function handling exceptions. This could occasionally lead to unexpected exceptions (@flash-gordon)