Use get in ns-requires since coll may be nil
Add special handling for {:refer {clojure.core :all}}

We will be emitting this separately as :refer-clojure
Docstring fixes
Add stitch/refer-clojure-from-map

Special emission of :refer-clojure for 'clojure.core
Pour rename maps into (sorted-map)
Ensure 'clojure.core is present in refer-clojure-from-map
Rewrite stitch/ns-from-map

Given regular data as input, ns-from-map can now produce much better ns
forms than before.
Add ^:unit tag to stitch unit tests
Remove newly unused code in slam.hound.stitch

Deleted code dealt mostly with parsing, which is now done in the asplode
step.