[UPDATE] add JSON parse and stringify transform stream tests.
[UPDATE] file read/write error handling. Initial tests for transform stream.
[UPDATE] added flow object tests.
[UPDATE] reorganized stream library. Moved external utilities to top-level directory.
[UPDATE] use graceful-fs npm module.
[UPDATE] added reduce stream test.
[UPDATE] rename test files.
[UPDATE] add stats count test.
[UPDATE] add max stream test.
[UPDATE] add min stats stream test.
[UPDATE] add stats sum stream tests.
[UPDATE] privatized reduce and transform methods.
[UPDATE] use strict. Add mean stats stream test.
[UPDATE] add variance stats stream test.
[UPDATE] input validation check.
[UPDATE] simplified tests.
[UPDATE] simplified variance stream test.
[UPDATE] add median stats stream test.