refactor: maintain abstraction
stricter param count checking
cosmetic: remove trailing whitespace
refactor: extract weave ports and container name into constants
explain that peer can be specified as fqdn and contain optional port

Closes #137.
validate CIDR
This isn't meant to be precise but supposed to guard against silly
mistakes.

Closes #116.
Merge branch 'master' into 130_launch_without_ip

Plus a bit of a refactoring, to avoid duplicating the CIDR
regexp. Plus some minor cosmetic tweaks.

Conflicts:
	README.md
	weave