Float rebuild button right instead of absolute positioning.

This allows h1 to flow around the button.

Fixes #216
Update generated integrity.css (issue #216)
Revert "moved htmlize and integrity.css to integrity.github.com"

This reverts commit 2fc097a6486b75df6fcf762ea28a01c53d2dcf3b.
Update issues url to github issues
Updated stylesheet from integrity.github.com repository
Update rakefile to build all files for documentation html
Add a section on documentation generation to integrity.txt
Merge pull request #218 from p/rebuild-button-overlap-2

Fix rebuild button overlap with h1
Add a smaller sized screenshot
Merge pull request #219 from p/reinstate-website-build

Reinstate website build in integrity repository
Write index.html rather than integrity.html when generating html documentation