TODO: add more tunable parameters

[IrvingF7]

Here, I record a few to-do items.

• Users can choose whether to use a previously acquired camera matrix. And whether this matrix is used to acquire a new camera matrix
• Users can use parameters to select what image-capturing system to use. Now it's fixed with usbcam.
• Users can decide whether the image-capturing systems save the image to disk or not.
• Users can choose what hand-eye calibration algorithm to use with parameter flags
• Study calibratecamera's flags a bit more to use suitable flags
• More comments and a proper README
• (Very ambitious) Maybe make a ceres solver version in the future, instead of relying on OpenCV.