parameterized schema

it would be useful to have higher order types defined which can be supplied with a parameter, such as:

```
$schema wrapper
$type
$object
$property-name "tag"
$property-schema $string
$property-name "contents"
$property-schema a
```
and this could then be applied in the following manner or similar:
```
$schema $start
$type
wrapper otherSchema
```
or
```
$property-schema wrapper otherSchema
```
This is particularly relevant when dealing with protocols where a default wrapper shape is mandatory across many request/response types. in my case, JsonWSP.

especially combined with the modular schema feature request this would allow us to express the

No files, tests, or entry points are named in the issue. Begin by locating the existing schema and type implementation and the related modular schema work; done means parameterized types can express the wrapper examples and be applied to request and response schemas.

Written by the indexing model from the issue text.