Update .gitignore
Add no-shrink generator combinator
Eagerly throw a helpful exception when elements is called on an empty collection

Prior to this change element will happily take an empty collection and
call gen/choose with 0 and -1, which apparently generates lots of 0s
and 1s, and then eventually throw an IndexOutOfBoundsException when it
eventually calls nth on the empty collection.
Merge pull request #35 from fredericksgary/elements-empty-error

Eagerly throw a helpful exception when elements is called on an empty collection
Add shrink-2 shrinking helper function
Merge branch 'feature/shrinking-helpers'

Conflicts:
	test/simple_check/core_test.clj
Add documentation for writing a Record generator
simple-check now Clojure/ClojureScript portable via cljx, fixes gh-11