Treat int64s as Strings.
Bug fix: misuse of private field in template.
Test case that fails before, but passes with the fixed private field bug.
No need to use internalGetPayload, just use the public getter.
Merge pull request #18 from alxhub/fix-clone-bug

Fix bug accessing the private field '_payload' in generated requests' clone() method.
Merge pull request #17 from alxhub/int64-as-string

Treat int64s as Strings.