WIP - Serialisable representation of CDefinition, Ctype, etc.

[keynmol]

At the moment there's a runtime exception related to recursive codecs

Exception in thread "main" java.lang.NullPointerException
        at scala.scalanative.runtime.package$.throwNullPointer(package.scala:203)
        at bindgen.CDefinition$$_lazy_implicit_$26$1.original$proxy9$1(CDefinition.scala:64)
        at bindgen.CDefinition$.$anonfun$32(CDefinition.scala:88)
        at bindgen.CDefinition$$$Lambda$60.apply(CDefinition.scala:24)
        at io.circe.derivation.ConfiguredEncoder$$anon$3.elemEncoders$lzyINIT3(ConfiguredEncoder.scala:81)
        at io.circe.derivation.ConfiguredEncoder$$anon$3.elemEncoders(ConfiguredEncoder.scala:81)
        at io.circe.derivation.ConfiguredEncoder.encodeElemAt(ConfiguredEncoder.scala:29)
        at io.circe.derivation.ConfiguredEncoder$$anon$3.encodeElemAt(ConfiguredEncoder.scala:80)
        at io.circe.derivation.ConfiguredEncoder.$anonfun$1(ConfiguredEncoder.scala:35)
        at io.circe.derivation.ConfiguredEncoder$$Lambda$1.apply(ConfiguredEncoder.scala:35)
        at scala.collection.Iterator$$anon$23.next(Iterator.scala:1035)

To fix this, we need to make the definition less recursive.