Added Indent CSS style to handle scope indentation.
Factored out binary op visitor, added syntax highlighting for keywords.
Added more syntax highlighting.
Implemented expand/collapse of nodes, used GitHub syntax highlighting.
Added highlighting of matched parens/braces/brackets on mouse hover, refactored various visitors/printing.
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Removed old code.
Simplified open_span overloads, ids for matched parens.
Further simplified/refactored HTML tag generators.
Fixed name collision in highlight matching IDs.
Merge pull request #403 from halide/html-improvements

HTML improvements