implement `containenv init` tasks about containment HOT 4 CLOSED

Consult issue #11 to discover the overall goal of these tasks.

from containment.

Tasks:

(0) construct target project path
(1) determine whether a target project exists (check for setup.py?)
(2) determine whether target project has previously been initialized (check for .containenv)?

If Initialized:

(1a) Exit with exception

Else uninitialized (assume git for the moment):

(2) mkdir .containenv
(3) Write appropriate container configs into PROJECT/.containenv/Dockerfile
(4) Write appropriate entrypoint.sh into PROJECT/.containenv/entrypoint.sh
(5) Write appropriate runcontainenv.sh into PROJECT/.containenv/runcontainenv.sh
(6) Build an image from the above with a reference (docker image tag) that is the absolute path (transformed to be a valid tag) to /FOO...BAR/PROJECT/.containenv
(6a) (optionally) publish said image

from containment.

@dangle I'm thinking of implementing each of the above tasks as a method of the Command class in:

containenv/containenv/containenv/cli/commands/init.py

from containment.

PR number #28 resolves this.

from containment.