styles.less: Style fixes

Two types of fixes:

  1) Comma separated selectors must be placed on the start of a line, so
     the selectors are all vertically aligned at column 0. Example:

       h1, h2, h3 {
         /* ... */
       }

     becomes:

       h1,
       h2,
       h3 {
         /* ... */
       }

  2) Assignments must always contain a space after the colon. Example:

       color:#000;

     becomes:

       color: #000;
styles.less: Add typography variables
styles.less: Remove unused selector
styles.less: Minor re-order
styles.less: Add further typography variables
styles.less: Add color variables
styles.less: Group into logical sections
Import compiled CSS stylesheet

Since the GitHub Jekyll configuration doesn't support plugins, we're
going to have to checkin our compiled styles.css file so that it can be
sourced by GitHub pages.