Small fixes, and make lines clickable to hide/show sections

Hello, and thank you for writing this.

I found some minor issues (warnings about font-lock-fontify-buffer, which should be replaced with font-lock-flush/ensure in later emacs versions, also the convention is to use "--" to identify internal variables/functions).

I also wanted to make the lines clickable, so that they would hide/show the sections of code separated by form-feeds. This is consistent with what I've seen in how most emacs packages use form-feeds: they logically separate sections of code.

There is one serious bug that I found: enable form-feed-mode, modify buffer, save buffer. The newlines right after the form-feeds will be gone, which is a corruption of the file. I had to turn off the cursor-moving function to fix this (see the commit), maybe there's a better way of doing it. Changing file contents with a "visual" minor mode is "not good".

What do you think?