Use custom deserialization to handle list extensions

[joshbooks]

intended to fix #7

[joshbooks]

@nitram22 mind taking a look when you have a minute?

[nitram22]

When I just tested it, the CertstreamCertificatePOJODeserializer threw a StackOverflow error.

Stacktrace:

Exception in thread "WebSocketConnectReadThread-18" java.lang.StackOverflowError at com.google.gson.internal.bind.JsonTreeReader.nextString(JsonTreeReader.java:178) at com.google.gson.internal.bind.TypeAdapters$29.read(TypeAdapters.java:702) at com.google.gson.internal.bind.TypeAdapters$29.read(TypeAdapters.java:723) at com.google.gson.internal.bind.TypeAdapters$29.read(TypeAdapters.java:698) at com.google.gson.internal.Streams.parse(Streams.java:48) at com.google.gson.internal.bind.TreeTypeAdapter.read(TreeTypeAdapter.java:65) at com.google.gson.Gson.fromJson(Gson.java:932) at com.google.gson.Gson.fromJson(Gson.java:1003) at com.google.gson.internal.bind.TreeTypeAdapter$GsonContextImpl.deserialize(TreeTypeAdapter.java:162) at io.calidog.certstream.CertStreamCertificatePOJODeserializer.deserialize(CertStreamCertificatePOJODeserializer.java:58) at io.calidog.certstream.CertStreamCertificatePOJODeserializer.deserialize(CertStreamCertificatePOJODeserializer.java:8) at com.google.gson.internal.bind.TreeTypeAdapter.read(TreeTypeAdapter.java:69) at com.google.gson.Gson.fromJson(Gson.java:932) at com.google.gson.Gson.fromJson(Gson.java:1003)

When reaching this line (56)
CertStreamCertificatePOJO retVal = jsonDeserializationContext.deserialize(jsonElement, type);

the deserialize() method is called again, which results in never executing the return retVal line (60) until the StackOverflowError is thrown.

This is from the JsonDeserializationContext doc for the deserialize() method:

Invokes default deserialization on the specified object. It should never be invoked on the element received as a parameter of the deserialize(JsonElement, Type, JsonDeserializationContext) method. Doing so will result in an infinite loop since Gson will in-turn call the custom deserializer again