Merge pull request #2 from okinoshima/master

update manual
improve message stream handling
support Builtin Command(cd, exit)
update to libzen 4d1acb1db93b3556d3940284ab9d8c225e4c299e
bug fix at completer
improve dshell command option
improve command compatibility
update to libzen 90ec8dccf37ecfc4a6e2d7cb4a2aed4ed2638eb3
refactor SubProc
drop support several redirect(1>&1, 1>&2, 2>&1, 2>&2, >&1, >&2)
update manual