Still to do (not necessarily all as part of this PR):
~Fix JsonSchema implementations for types in third-party crates~
Remove now-unnecessary preserve_order feature flag
Where we currently use a single-valued enum, instead use const (check which schema versions support const - may require a new visitor to change const to enum)
Fix deriving JsonSchema on large types, ensure compile times are OK
Reduce usages of json!/json_schema! for better performance, particularly in schemars_derive
Implements #242
Still to do (not necessarily all as part of this PR):
JsonSchemaimplementations for types in third-party crates~preserve_orderfeature flagenum, instead useconst(check which schema versions supportconst- may require a new visitor to changeconsttoenum)JsonSchemaon large types, ensure compile times are OKjson!/json_schema!for better performance, particularly in schemars_derive