Added AVL tree implementation to moorings, based tree-set on top of it
Adding oracle-style tests for sets
Improved set tests
Adds string-to-list function to moorings
range-by implementation, based string-to-list on top of it
data structures for http/url
adding syntax for datatype: tokenizer (with constructor), grammar (datatype), ast (both pyret and racket: datatype, new variants, constructor), parser (datatype, variants, constructor), and parse tests (all pass except for the tests that use desugaring, as that hasn't been written yet)

Conflicts:
	src/lang/grammar.rkt
desugaring of datatype working on toy examples
datatype working
better comment on use of desugar in types-compile
add syntax highlight via codemirror to the examples on the pyret.org site
add missing changes in page-template for code highlighting
only highlight on homepage
Merge branch 'highlighting-examples'
simplify derivative
Merge branch 'master' into datatype
fold_n base and regression
desugaring data to datatype
remove redundant comment, extraneous nothings
fix fold_n