Allow for marshalling schema to JSON for storage

[brocococonut]

Having the ability to convert a properly formatted JSON string into a schema is great. But it'd work better if the reverse were also possible. Currently if you try to run a schema through json.Marshal, you get something similar to this:

schema := vjson.NewSchema(
	vjson.Float("i").Required(),
	vjson.Array("children", vjson.String("item")),
)

byteStr, _ := json.Marshal(schema)

println(string(byteStr)) // Output: [{},{}]

Having complimentary functions to vjson.ReadFromBytes(), vjson.ReadFromString(), vjson.ReadFromFile() such as schema.WriteToString(...), schema.WriteToBytes(...), and schema.WriteToFile(...) would enable the proper backing up and restoring of these schemas.

[miladibra10]

I will review the PR ASAP.

[miladibra10]

Dear @brocococonut
Your requested feature is implemented. you can use json.Marshal method in the standard library in order to create a backup of your schema.