Update CSS for DuckDuckHack Docs code snippets
- Reduce font-size to 12px from 14 for narrower code blocks
- Switch to better, cross-platform font-stack
- changes only affect docs pages, based on duckduckhack-docs class on
  <body>
make monospace font-stack global for all pre/code/tt elements
Make inline codeblock more visible with background and padding
Merge pull request #2 from duckduckgo/zaahir/docs-syntax-highlighting

Update CSS for DuckDuckHack Docs code snippets