Breaking change, default behavior is `:root`

• removes :root, this is the default behavior when specifying packages
• removes :noroot, and replaces it with :deps
• adds :all, to select all the dependencies
• adds :main, to select main pacakges

When using the expression syntax, the first usage is often to target
all the roots and the dependencies... however most subtractions use
:root.

Usage before:

goda graph X - golang.org/x/tools/...:root - github.com/xyz/...:root

Usage after:

goda graph X:all - golang.org/x/tools/... - github.com/xyz/...