Add benchmarks

[JimmyCushnie]

Performance is not a focus of this project, but of course it'll ideally be as fast as possible, and ideally we never introduce any regressions to performance. To keep track of performance and in particular to track changes to performance across changes to the code, I intend to add a SUCC.Benchmarks project. This project, a lovely companion to the existing SUCC.Tests, will contain stress-testy benchmarks for various aspects of the library, including serialization and deserialization of all the different types, parsing files, and saving files.