Setup CI workflows for project

[kbuffardi]

Using GitHub Actions, set up the following continuous integration workflows:

• When code is pushed to the main branch or a pull request is made for it, make sure that the code compiles successfully. Add a status badge in README.md that reflects the current status of the main branch's build.
• When a pull request is made for the main branch, check the style of all .cpp and .h files using cpplint