Gentoo support added by Dan Molik dan@d3fy.net 2014-09-03

Cwtool changes made to autodetect portage, eix, and openrc.
Extensive use of eix to limit the invocation emerge, as traversing
the package tree is expensive.

All cwtool functions have been implemented. The pkg-latest function
will need upstream support to query remote repositories.
Merge pull request #2 from GrayTShirt/master

Gentoo support added by Dan Molik dan@d3fy.net 2014-09-03