Clarify docstring for hesokuri.hesobase namespace
Clean-up in write-tree and write-blob functions

- Rename write-tree* to write-tree, since write-tree never existed.
- Take advantage of clojure.java.io/copy's ability to copy Strings to
  OutputStreams in hesokuri.git-test.
- Correct documentation in write-blob and write-tree about values that are
  used by passing to clojure.java.io/copy. Docs said any value accepted by
  cjio/input-stream is valid, but copy actually has different semantics and
  accepts fewer types.