Minimal create-astro CLI

[natemoo-re]

Changes

Adds an extremely minimal create-astro CLI to scaffold out our new starter. It will need to be more robust (and have a better method for keeping the starters in sync), but I just wanted to get something quick out.

cc @kevinkassim

Testing

cd create-astro
npm link
cd ../..
npm init astro my-awesome-project

No tests. This is extremely temporary!

• Tests are passing
• Tests updated where necessary

Docs

Working on these now.

• Docs / READMEs updated
• Code comments added where helpful

[matthewp]

lgtm