Remove serialization attributes

This pull request removes the serialization attributes and adds basic support for error handling. Essentially it will be part of a series of small pull requests related to #5.

Please rename to `parse`. Qaiain follows the de-facto naming convention for F#, which is to use camel-case for function names. I know that's not what the official documentation says, but it's what most F# code looks like - even code being developed today...

(F# code that should be exposed to other .NET languages should still follow the normal .NET coding conventions, but those mostly apply to classes and their members.)