Dont strip as comments

[dandavison]

See #125

This PR contains test cases and fixes for a bug relating to inline comments on import ... as ... lines.

Examples of the incorrect behavior are (all invocations of isort are with default options, i.e. isort -d $file):

Example 1

from a import b as bb  # b comment
from a import c as cc  # c comment

On 3.9.0 this has its comments stripped; with this PR it is left unchanged.

Example 2

from a import b as bb  # b comment
from a import c as cc  # c comment
from a import d

was being converted to (branch develop 3.9.0)

from a import b as bb
from a import c as cc
from a import d  # b comment; c comment

with this PR it is left unchanged.

Note that there is an option 'combine_as_imports' but it is not (AIUI) exposed to the user in the command line API. If that option is set to True by manually editing isort/settings.py, we do get the desired output for these examples (one of the test cases confirms this).

from a import b as bb, c as cc  # b comment; c comment

from a import b as bb, c as cc, d  # b comment; c comment

[timothycrosley]

This looks great! Thank you!