6.0.2

CHANGES:

• adapt to mirage-flow 4 changes (add shutdown, alias to close) (#143 @hannesm)
• remove ppx_cstruct and sexplib and ppx_sexp_conv dependencies (#143 @hannesm)
• update to cmdliner 1.1.0 changes (#143 @hannesm)
• use oUnit2 (#141 @Alessandro-Barbieri)