Add instances for 'unordered-collections' data types

[JordanMartinez]

Looking at unordered collections, these types should have instances as well:

• HashMap
• HashSet

[thomashoneyman]

@JordanMartinez I agree those data types could use instances. As a matter of policy, though, thepurescript-contrib libraries only include dependencies from purescript or purescript-contrib. That way they can always be maintained by contributors without needing to wait on outside repositories to update. For example, we can guaranteed update all libraries in those two organizations for compiler releases even if other library authors aren't available at the time.

[JordanMartinez]

Makes sense!