Retainer

Retainer is used at run time in 5 crates. It's used only as a dev dependency in 1 crate.

Depender (with downloads and own rev deps)			Retainer version
270		rencfs		^0.3.0
		werkbank		^0.3.0
		force-rss		^0.3
		kapiti		^0.3
		fast42		^0.3
13K	2	ssh-agent-lib	dev	^0.3.0