Remove unused images and losslessly compress the rest.

public/images/code_bg.png          | Bin 8501 -> 6790 bytes
public/images/code_example_bg.png  | Bin 142 -> 92 bytes
public/images/code_heading.png     | Bin 3832 -> 2977 bytes
public/images/download-button.png  | Bin 11660 -> 8861 bytes
public/images/fork_less.png        | Bin 22742 -> 17394 bytes
public/images/header_bg.png        | Bin 177 -> 133 bytes
public/images/header_highlight.png | Bin 11470 -> 9974 bytes
public/images/less_description.png | Bin 10050 -> 9039 bytes
public/images/logo.png             | Bin 13831 -> 12991 bytes
public/images/ruby.png             | Bin 19627 -> 18715 bytes
public/images/sub_header_bg.png    | Bin 153 -> 112 bytes
public/images/tab_left.png         | Bin 407 -> 365 bytes
public/images/tab_right.png        | Bin 582 -> 512 bytes
public/images/tweet_about_less.png | Bin 16532 -> 15027 bytes
public/images/twitter3.png         | Bin 3078 -> 2096 bytes

Also, add forkme_left_red.png in the repo and optimize it.
Add alt text and image dimensions for download-button.png.
Remove type="text/javascript".

This is no longer needed for HTML5.
Remove trailing spaces and extra newlines.
Fix a few JSHint warnings.
Include less.js after all the css files.
Use https for the Github links.
Remove the unused Twitter script.
Remove unit from zero.
templates/layout.rhtml: Minor html5 fixes.
Include html5shiv.js for older browsers.