Make text belonging to a form element a label

Put <label for="...">...</label>¹ around the labels describing a form
element so users may click on it to toggle a checkbox or jump to a
textarea or so.

[1]: https://developer.mozilla.org/en-US/docs/Web/HTML/Element/label
Merge pull request #1 from yath/label

Make text belonging to a form element a label
Add github URL to about template

Add link to https://github.com/formorer/paste.pl to templates/about so
possible contributors know where to put their pull requests. :)
Merge pull request #2 from yath/about_github

Add github URL to about template
Don't use prototypes
Fix comments in hidden pastes
Bould langugage id detection