[TASK] Make changes to allow the project to be build-able on Mac

## Task Context

At the moment, the project is structured in a way to be compiled and built on a Linux machine. It would be nice to allow for the project to be easily build-able on Mac machines as well.

## Acceptance Criteria

This completion of this task should allow for Macs to build this project without many complications. It'll be nice to have some code in place that checks the current operating system and changes the control flow of what libraries to pull from accordingly.

This will likely come in the form of a mixture between updating the cmake and src file. It will also be good to have a step by step instruction guide on how to build this project on Mac somewhere in the docs.

Two issues I've noticed on Macs include the inclusion of `argp` and `bsd` in this project. This may be solved by using [argp-standalone](https://formulae.brew.sh/formula/argp-standalone) and [string.h](https://www.tutorialspoint.com/c_standard_library/string_h.htm) instead, but other solutions may be better/valid as well.

## Additional Context

This Github thread may be useful for how to get `argp-standalone` properly linked on Mac: https://github.com/AltraMayor/f3/issues/42#issuecomment-221746635

A follow up issue to this later on would be to also add a Github action that builds the project on a Mac machine. However, this is not required for this current task.

Please read through the [Contributing to the Project](https://github.com/jmakhack/myanimelist-cli/blob/master/CONTRIBUTING.md) document before working on this project.

Read CONTRIBUTING.md and the CMake configuration first, then reproduce the argp and bsd build issues on macOS. Inspect the relevant C source files and the linked argp-standalone guidance. Done means the project builds on Mac, selects appropriate platform dependencies, and includes step-by-step Mac build instructions.

Written by the indexing model from the issue text.