switch some bits of the code to analogue functions as per suggestion in #3
overwrote one of Simon's changes; simplify the Stratiplot() call
various edits, including fixing some pandoc markdown superscripts; missing parentheses; phrasing etc
Merge pull request #9 from gavinsimpson/add-analogue

Add analogue code to simplify a couple of code chunks
Merge pull request #10 from gavinsimpson/gav-edits

various edits, including fixing some pandoc markdown superscripts; missi...