When printing a pointer, only elide the type for unnamed pointers.
Otherwise, we can run into situations where named and unnamed pointers
format the same way in indistinguishable ways.

When printing an interview, never skip the interface type.
Whether we skip printing the type should be determined by the
parent containers, and not locally determined.
For examples, interface values within a struct, slice, or map
will always be elided since they can be inferred.

If a slice of bytes is mostly text, format them as text
instead of as []byte literal with hexadecimal digits.

Avoid always printing the type. This is technically invalid Go code,
but is unnecessary in many cases since the type is inferred
from the parent concrete type.

Fixes #272

Versions older than Go 1.13 are no longer in use. Remove unnecessary
dependencies.