Adds the ability to output control characters

[dtwilliamson]

ASCII < 0x20

Adds Keyboard.press(KEY_LEFT_CTRL), etc., to sendVal()

[Chris-Johnston]

I'm not sure if I made the whole line endings thing worse or not. Please let me know if I screwed it up. I added the .gitattributes file in 26ebf8e that should at least make things consistent. I'm just sticking with CRLF for now because that's what Visual Studio / Visual Micro likes.

[Chris-Johnston]

As for 80419a1, this raises a few issues. (In the future this might be easier to manage this in a different PR)

• It is now impossible for users to enter any characters < 0x20, including CR, LF, escape, backspace, and tab.
• There is no on-screen representation of printing L_CTRL + Character. (This is an easy fix)
• The keyboard would no longer be using a standard ASCII table. Documentation should probably provide this modified table. (At that point, what if the keyboard used an entirely custom table based off of ASCII? It would be like a keymap but with 256 combinations! Could do all sorts of things with that.)

[dtwilliamson]

If you enter a character < 0x20 without my change, most get changed to null by the Keyboard lib so nothing gets output to the computer. With my change, those characters get converted to their Ctrl key equivalent. (Ctrl-M is CR, Ctrl-H is backspace, etc.). The reason the Keyboard lib does this is because it functions like a USB HID keyboard. While it supports a few common keystrokes which map to keys on a keyboard, it doesn't pass others (like Ctrl-C for example). With my change, they all work. A more complex change would be to directly support the few keys that map to a keyboard and include a modified version of my change to handle the others. My change as it stands is simpler and works for all characters below 0x20.

My change does use a standard ASCII table. Ctrl characters are simply CHAR - 64 (I have to use 96 because the Keyboard lib sees the uppercase chars as shifted).

http://man7.org/linux/man-pages/man7/ascii.7.html

https://github.com/arduino-libraries/Keyboard/blob/master/src/Keyboard.cpp#L88

https://www.arduino.cc/en/Reference/KeyboardModifiers

https://en.wikipedia.org/wiki/Control_key#History (zeroing the left two bits of a seven-bit word is the same as subtracting 96)

[Chris-Johnston]

Thanks for the clear reply; I now see how this works. I think it would be worth adding a modification for Backspace, Tab, and LF, so that they still work independent of OS or environment. The other ones work fine.

[dtwilliamson]

I added code to display chars below 32 on the OLED. I also implemented the HID mode and made it configurable so a user can select HID or pure ASCII handling of lower characters

[Chris-Johnston]

This is awesome. Everything works as expected, and I appreciate the the level of detail that you have put into the screen output. Thank you! I will be updating code comments and README to provide credit for your work.