NXTCHPTR per damianoR

When I was reading manga changing chapters required the use of my mouse and I was searching for a way to do it on the keyboard instead, long story short I didn't find it, so I wrote this on a whim for personal use. If anyone else feels the necessity I felt, feel free to use it.

Also, I set it to work on readmanganato.com, bcs that's where I read.

Known bugs: actually it's not a bug, I just don't need to read bonus chapters, so the ones ending with .5 etc.
Btw, "next chapter" for the addon basically means 103->104 even if there's a 103.5. Useless chapters, i don't even want to "fix" this, it's a feature.

If you want me to do some changes you can contact me on Telegram, my username is @damianor.