PR: Add registers

[bgallois]

Added basic vim registers:

• Numbered registers
• Small delete register
• Normal register with lowercase letters
• Append to normal registers with uppercase letters

[ccordoba12]

This looks very interesting! I didn't know that Vim has this feature:

https://www.brianstorti.com/vim-registers/

Just out of curiosity: do you plan to implement the read only registers "., "%, ": and "# as part of this PR?

[bgallois]

Yes, it's a very useful feature. I plan to implement the read-only registers latter when I will have time, so it will be for another PR.