Describe Template.__hash__() behavior in the spec. (And verify we like Template.__eq__().)

[davepeck]

Given our definition of Template.__eq__(), probably it falls out as:

class Template:
    def __hash__(self):
        return hash(self.args)

class Interpolation:
    def __hash__(self):
        return hash((self.value, self.expr, self.conv, self.format_spec))

Which implies that Template is only hashable if all of its values is.

But @lysnikolaou perhaps something different will fall out of implementation?