Completion false positives for snakemake.io, etc.

[iromeo]

Current completion implementation adds all top-level methods from snakemake.io to autocompletion, although snakemake imports only some of methods, e.g.

See

# ~/anaconda/envs/snakemake/lib/python3.6/site-packages/snakemake/workflow.py
from snakemake.io import protected, temp, temporary, ancient, directory, expand, dynamic, glob_wildcards, flag, not_iterable, touch, unpack, local, pipe, repeat, report

E.g. contains_wildcard_constraints method shouldn't be visible in autocompletion. We need smarter impl. Related to #1

[iromeo]

We need to emulate from snakemake.workflow import * to resolve this