Path dependencies

[LPGhatguy]

Sometimes, it's useful for projects to depend on versions of a tool that isn't managed by Foreman. This comes up when working on tools like Rojo, where I want to use the master branch by default, not any stable release.

To solve this, we could add path dependencies to Foreman, like:

[tools]
rojo = { path = "~/.cargo/bin/rojo" }

Are there any security concerns with this approach? Being able to run any binary on a user's system might be dangerous, and we might want to lock this down to the system config only.