Add direct path for install

[ajfisher]

Provide the mechanism to point at:

• git+https:///
• package@x.y.z
• file://

As alternative methods for interchange install ...

This will allow packages that aren't formally part of interchange to be included as necessary so long as they comply with the structure (eg manifest files etc).

[ajfisher]

Status:

git+https:// currently works

Todo:

package@x.y.z from npm
file path.

Possibly use switches to account for the ambiguity of naming with these.