style changes to labs 1, 2, 3

added horizontal line before OYO
changed numbering in OYO from lazy to unordered with - and three spaces
changed formatting of probability equations in lab 2 to Latex with [\ \] that displays nicely
added line to style guide about backticks
Merge pull request #4 from naomilong/master

style changes to labs 1, 2, 3