FromJSON and ToJSON instances

This module defines FromJSON and ToJSON instances for Bond abstract syntax tree. They allow using the aeson library to encode Bond AST types to JSON format:

> encode (Bond [] [Namespace Nothing ["example"]] [])
"{\"namespaces\":[{\"name\":[\"example\"]}],\"imports\":[],\"declarations\":[]}"

and decode Bond data types from JSON:

> decode "{\"namespaces\":[{\"name\":[\"example\"]}],\"imports\":[],\"declarations\":[]}" :: Maybe Bond
Just (Bond {bondImports = [], bondNamespaces = [Namespace {nsLanguage = Nothing, nsName = ["example"]}], bondDeclarations = []})