Add --targets to CLI

[aardschok]

Solves #334

• Added --targets through publish
• Added check for PYBLISH_TARGETS env variable
  if targets are found register them with the API
• Minor cosmetics

[tokejepsen]

Looks good to me. Maybe we need some tests for this?

[aardschok]

I'll setup a test for targets

[tokejepsen]

Looks good to me. @mottosso ?

[mottosso]

This is too short of a variable name.

Can we also make it..

if not target:
  continue

register_target(target)

To reduce indentation?

[mottosso]

Alternatively..

register_target(target) if target else None

[aardschok]

If I do that then I want to change the lines (line 150) above it as well to have consistency.
I used this as a template to ensure the logic would be the same:

# Register hosts from environment "PYBLISHHOSTS"
for host in os.environ.get("PYBLISH_HOSTS", "").split(os.pathsep):
    if host:
        register_host(host)

These lines would then become:

# Register hosts from environment "PYBLISHHOSTS"
for host in os.environ.get("PYBLISH_HOSTS", "").split(os.pathsep):
    if not host:
        continue
    register_host(host)

Agreed?

[mottosso]

Ok, with that minor tweak I'm happy.

[mottosso]

Thanks!