Merge pull request #59 from kmicklas/master

add image-height to the image library bindings
avast!
Merge branch 'master' of github.com:brownplt/pyret-lang
Add Pyret function 'read-sexpr' : string -> nested-lists.
* e.g. usage: read-sexpr(" (++  () 987 \"str\") ") is [["symbol", "++"], [], 987, "str"]
* limitations: no negative or decimal numbers;
               no string escapes;
               no numbers in identifiers
zero one infinity
Merge branch 'master' of https://github.com/brownplt/pyret-lang
read-sexpr: Clean up code; allow digits in identifiers; allow sign and decimals in numbers.
read-sexpr: throw proper Pyret errors.
fix syntax examples for raise