meta model should capture base request, response and notification types

[karthiknadig]

The meta model should have a description of the base request, response and notification types. It should also capture the ranges allowed as per LSP description for the various numeric types.

[dbaeumer]

The description of the base types I left out on purpose since I don't want to define how language should implement JSON-RPC. Some implementations might simply use existing libraries.

The ranges of the numeric types are implicitly given by the fact that the meta model uses special type names for them. Adding range description can therefore only be documentation.