Drop markdown code fences

The markdown parser used by GitHub does not support code fences (triple
backticks). Drop them. In their stead, use either standard markdown code
intentation or tags provided by Liquid. (Jekyll uses Liquid for interpreting
templates.) In cases where syntax highlighting is desirable, use Liquid tags;
otherwise, use standard indentation, as indentation is easier to read.
Merge pull request #1776 from SatelliteQE/syntax-highlighting

Drop markdown code fences