Sets up a new V project

Usage:
  v new [NAME] [DESCRIPTION]

Sets up a new V project with a 'v.mod' file, and a 'main.v' "Hello World"
file, and performs 'git init' (if git is installed on the system).

If NAME is given, the project will be setup in a new directory with that
name, and that name will be added to the 'v.mod' file. If no name is given,
the user will be prompted for a name.

If DESCRIPTION is given, the 'v.mod' file is updated with said description.