This change removes some ambiguity that existed in MuIL tokens given the
simplistic naming scheme of only using "/" as a delimiter. We could have
resolved this ambiguity through successive name bindings, but I prefer a
more deterministic approach. A module member token now delimits the
package/module name from the member name by a ":" character, as in
"aws/ec2:VM". Furthermore, when reexporting elements from the current
package/module, we will use the self-referential "." character, as in
".:VM".
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