Add Unit Test Framework

[AddressXception]

Feature Request

Is your feature request related to a problem? Please describe.
The current testing pattern involves using cmake test to execute the examples/simple and examples/api programs respectively. While this is useful for demonstrating the workflow of executing an election, it does not easily demonstrate the expectations of individual functions, particularly the encryption and decryption processes.

Describe the solution you'd like
Choose a common, actively maintained, and lightweight unit testing framework for C and add initial unit tests to test both high level and low level API's that demonstrate a pattern contributors should use when adding tests. A sufficient unit test framework should demonstrate a common testing paradigm such as setup, teardown, and test_<description>

Describe alternatives you've considered
Another alternative would be to build a basic testing framework from scratch. For a variety of reasons it may be better to source a solution from the community.

Teachability, Documentation, Adoption, Migration Strategy
Ideally consumers of this library would be able to execute the existing example applications to demonstrate a complete working sample; but also execute individual tests to verify specific steps of the process.