Fixed and improved form-wise evaluation

• Fixed escaping things as they're sent across the prepl, was causing some subtle bugs when you had a bunch of \\\\ in use.
• Fixed #4 and improved it a lot. So now if no form is found nothing happens and it handles every case I could throw at it.

The eval current / outer form issues were caused by some of the Neovim API being 0 indexed and some being 1 indexed. So some values have to be decremented or incremented in different cases while hunting for matching (){}[] pairs of forms. That function was hard to get right but it works well in every case I can think of now!

Next up is a bunch of repo changes around documentation and then probably an initial autocomplete. Maybe some configuration as mentioned in #5, feel free to add your feedback there too!