added inline monospace and colorize source block

I added some highlighting that I currently use in vim. 
We should avoid using any concrete colors in the stylesheets. People can use different syntax themes (dark and light) and usually "hardcoded" colors hurt readability and don't meet people's expectations out of their preferred themes. For example this is how orange looks with very popular Solarized Light theme (orange - top, default color - bottom):
![before_after](https://cloud.githubusercontent.com/assets/182853/4882621/7c166d4a-6358-11e4-8157-705d06b097d4.jpg)

Usually we try to re-use existing standard LESS variables or CSS classes to highlight things. For example this is what we do for headers:

```less
.markup.heading {
  font-weight: bold;

  // Lighten headers for dark themes.
  & when (lightness(@syntax-background-color) < 50%) {
    color: lighten(@syntax-text-color, 20%);
  }

  // Darken headers for light themes.
  & when (lightness(@syntax-background-color) > 50%) {
    color: darken(@syntax-text-color, 20%);
  }
}
```
We make color darker for light themes and brighter for dark themes. I think we should leave `.support` as is, since it's a standard CSS class and decent syntax themes should provide custom color for it.