Named errors

[MiguelSavignano]

#12

Create a new errors class

PatchInvalidOperationError
PatchMissingTargetObjectError
PatchTestNotEqualError
PatchMissingKeyError

Example:

operations = [{"op": "replace", "value": "BAZZ"}]
item = {foo: "bazz"}
JSON::Patch.new(item, operations).call
# => JSON::PatchMissingKeyError (Missing key: path)

operations = [{"op": "replaces", path: "/foo", "value": "BAZZ"}]
item = {foo: "bazz"}
JSON::Patch.new(item, operations).call
# => PatchInvalidOperationError