Support Recursive Vendoring

[nathanielc]

Would you consider supporting vendoring dependencies of dependencies? This way 100% of all dependencies for a project can be vendored.

This should probably be an optional argument -r or something:

# Query all deps recursively
manul -Q -r
# Install all deps recursively 
manul -I -r
# update all deps recursively
manul -U -r
# remove probably shouldn't support the recurse option, just use clean after remove if needed
# clean all unneeded deps taking into account recursive deps.
manul -C -r
# clean all unneeded deps taking into account only top level deps. This would remove all vendored recursive deps
manul -C

[kovetskiy]

@nathanielc Please check it now.