Update for week 3 of Milestone 3

Last week I managed to do the following tasks for #SAOC2020:
- added comments in the code
- started the gcalendar implementation
- started to implement an interface for gdrive library, to make it easy to use and the code exposed to the user to be the same as the code for the libraries used in other languages. For example, in java to get the informations about the user, user's drive and system capabilities, you do something like this:

About result = drive.about().get().setFields("*");

Now, the D library request looks the same.

The plan for the next week:
- continue the implementation of the interface
- continue the implementation of the gcalendar library

Milestone 1 updates: [0]
Milestone 2 week 1: [1]
Milestone 2 week 2: [2]
Milestone 2 week 3: [3]
Milestone 2 week 4: [4]
Milestone 3 week 1: [5]
Milestone 3 week 2: [6]

[0]: https://forum.dlang.org/post/eaefvlbgikujonfjjzqi@forum.dlang.org
[1]: https://forum.dlang.org/post/jezqwzpeknpxhmqgkewe@forum.dlang.org
[2]: https://forum.dlang.org/post/kffvsmmxrkftxlbqklsd@forum.dlang.org
[3]: https://forum.dlang.org/post/yvbnsycuxqjfxghqajbu@forum.dlang.org
[4]: https://forum.dlang.org/post/jwasbvtjbofftybnsqro@forum.dlang.org
[5]: https://forum.dlang.org/post/gimihhnxzbkeodvrotoy@forum.dlang.org
[6]: https://forum.dlang.org/post/qfpwiuyojozzkvdfkive@forum.dlang.org