Added remap support for hotkeys (backlight brightness, screenshot, etc) and ability to disable certain hotkeys

[Starbit04]

I tried remapping X to B on my 3DS and realised it conflicted with the hotkeys for controlling the backlight, so I decided to make a fix by adding an option to enable/disable the backlight hotkeys, along with the screenshot hotkey for consistency.

I then added the ability to remap each existing hotkey to a different button combo, since I noticed some people were wanting it (#202 and #172) and seemed like a better solution to the initial problem. I've still kept the option for disabling the hotkeys though, since it could still be useful for who wouldn't want to adjust the backlight in-game or take screenshots.

This is the first time I've done a pull request for an open source project, so apologies if there's something I haven't done correctly. I've compiled and tested my changes on real hardware (original 3DS XL) and all seems to be good, and I've updated the readme to reflect my changes.

[NeoByt3]

Hey I was wondering if you'd be able to provide the compiled firm file for this version you've created as I have zero knowledge on how to compile this myself.

[Starbit04]

Hey I was wondering if you'd be able to provide the compiled firm file for this version you've created as I have zero knowledge on how to compile this myself.

Hi, I've added a build to my repo

[NeoByt3]

Thanks!