Refactor/client callbacks

[dmin12]

Refactored the client class to streamline structure & logic.

Previously, the client class had static callback functions, which referenced static flags and variables. These static methods and variables were converted into member variables of Client. As a workaround for GLFWwindow requiring static function callbacks, all of the member callback functions are bound to a lambda, which essentially just wraps around the Client callback functions. These lambdas reference a GLFW user pointer through glfwGetWindowUserPointer(window), and this user pointer is bound to an instance of Client.

Client::idleCallback() was refactored by removing the call to Client::handleKeys(), instead moving that logic to the Client::keyCallback(). The proposed structure for input handling is as follows: for inputs that are continuous (i.e. movement, jumping), keyCallback() will set a flag, which is separately handled in idleCallback(), and for inputs that are press/release or single press (i.e. left shift for sprint), the event is sent directly in the keyCallback(), which avoids using flags for checking if events were already sent.

Also fixed some bugs with camera movement logic and added a simple window resize callback.

Added documentation for client.hpp and camera.hpp.

[Tyler-Lentz]

I really like all these changes, thanks for grinding these out