Functions to construct interceptors dynamically.

The functions with names that end in '-action' compile Pedestal
interceptors. These are the main public entry points, and are used
by the `literals` namespace when loading Vase descriptors.

Take care to avoid code generation during request processing. It is
time-consuming, so it should be done at application startup time
instead.

Actions are created by emitting code (in the functions named
`-exprs`) which gets evaluated to build an interceptor. Arguments to
the `-exprs` functions are interpolated into the emitted code. These
arguments can contain literals or one s-expression each.

For example, `respond-action-exprs` has an argument `body` that will
be used as the HTTP response body. It may be a string or an
s-expression.

When s-expression arguments are evaluated, they have some bindings
available in scope:

- `request` - contains the Pedestal request map
- `context` - contains the Pedestal context map
- request parameters captured from path-params or parsed body
  parameters _and_ named in the `params` seq

E.g., if `params` holds `['userid]` and the request matched a route
with "/users/:userid", then the s-expression will have the symbol
`'userid` bound to the value of that request parameter.

Contains the clojure.spec definitions for the Vase
application specification.