Support drop-in replacement of MIT libraries for managed platforms

[SteveSyfuhs]

This library should be drop-in compatible with MIT Kerberos within a (managed) application.

This requires supporting the following MIT features:

• Configuration file parsing and generation for client, server, and potentially KDC (https://github.com/dotnet/Kerberos.NET/issues/126)
• Cache file parsing and generation for client (https://github.com/dotnet/Kerberos.NET/issues/160)
• GSS-API (https://github.com/dotnet/Kerberos.NET/issues/54)

Some optional work:

• Command line tooling for manipulating above? Kinit/klist?
• Windows interop with LSASS for loading keys?

[SteveSyfuhs]

PR #176 adds cache file support and would close #160. #126 has the ability to read the configuration today, but at the moment the library doesn't actually use the configuration. Whatever additional work thats added to glue this together should tap into the cache support to make it a complete e2e configurable solution.