Implement API in the C library

[pamtaro]

Checklist

🚨Please review the guidelines for contributing to this repository.

• 🤔 CONSIDER adding a unit test if your PR resolves an issue.
• ✅ DO check open PR's to avoid duplicates.
• ✅ DO keep pull requests small so they can be easily reviewed.
• ✅ DO build locally before pushing.
• ✅ DO make sure tests pass.
• ✅ DO make sure any new changes are documented.
• ✅ DO make sure not to introduce any compiler warnings.
• ❌AVOID breaking the continuous integration build.
• ❌AVOID making significant changes to the overall architecture.

Description

This introduces an api layer to the C library which can be used to execute the entire election via single api methods to create election/key ceremony, encrypt ballot, register ballot, record cast/spoil ballot, and tally votes. It is based on the simple election's examples, but with adjustments to the flow to more approriately fit real eleciton scenarios and with signatures adjusted to allow for Interop marshalling via PInvoke from the C# wrapper sdk side. This also adds the api version to the examples folder as an alternative executable that can demonstrate an end-to-end election.

NOTE: This contains and should be merged after PR #42

closes #33
closes #34
closes #35
closes #36

[AddressXception]

Looks good. Since we adjusted the create election workflow to use the new classes here, should we either:

1. remove the examples/simple/main_keyceremony.h and corresponding implementation, or
2. modify examples/simple/main.c to include both initialization workflows (so it's clear the simple election tests can be executed using both setup methods)?

[pamtaro]

Looks good. Since we adjusted the create election workflow to use the new classes here, should we either:

1. remove the examples/simple/main_keyceremony.h and corresponding implementation, or
2. modify examples/simple/main.c to include both initialization workflows (so it's clear the simple election tests can be executed using both setup methods)?

I think I prefer to keep both examples around.. maybe I should create an api_simple example and use the API approach in that instead of trying to reuse the existing simple example 🤔