makes numbers in functions example (restaurant bills) nicer
adds explanation about comments in Clojure code
makes vector exercise simpler
replaces mentions of 'symbol' with 'name'
renamed slides chapter title 'Function library' -> 'Common, core functions'
examples of < with more than 2 args
changes = example to not use maps (not discussed yet)
updates intro to maps slightly (commas optional, removes into fn ex)
visually demarcates nil from boolean values in slide
adds a needed hint to 2nd maps exercise
adjusts wording