cmake standalone build

[franziskuskiefer]

Fix CMake standalone builds and add an example for how to use hacl packages in a cmake project. The way the includes work isn't great. Follow ups

• [ ] Let's make this easier to use (include paths)
• [ ] Update the example
• [ ] Add the example to the book

For reference: https://github.com/danwallach/electionguard-kotlin-multiplatform/issues/200

[coveralls]

Pull Request Test Coverage Report for Build 3584836974

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 53.985%

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Totals
Change from base Build 3564982264:	0.0%
Covered Lines:	33230
Relevant Lines:	61554

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💛 - Coveralls