This checkin continues progress on marapongo/mu#9. It's still not
complete, however we're getting there. In particular, this includes:
* Rename of ComplexLiteral to SchemaLiteral, as it is used exclusively
for schematized types. Also includes a set of changes associated
with this, like deep value conversion to `map[string]interface{}`.
* Binding of schema types included within a Stack. This allows names in
type references to be bound to those schema types during typechecking.
This also includes binding schema properties, reusing all the existing
property binding logic for stacks. In this way, properties between
stacks and custom schema types are one and the same, which is nice.
* Enforcement for custom schema constraints; this includes Pattern,
MaxLength, MinLength, Maximum, and Minimum, as per the JSON Schema
specification.
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