Revert "Some refactoring; support for https://github.com/timmolter/XChange/issues/114"

This reverts commit e90ae78fc14fe8b7833b05aa371f79ec38721ff1.
Revert "Refactor digesting"

This reverts commit f96481b6a667590bb14039809770745949be1f74.
Revert "Refactor: separate method metadata from invocation parameters"

This reverts commit 0424268ca8a209ea4bc3746708936a5ce59630b0.