Keep unused import and pass statement

[adhikasp]

Make it possible to provide CLI args to keep autoflake from removing useless pass (--keep-useless-pass) and unused import (--keep-unused-import)

Closes #13 #10

[coveralls]

Coverage increased (+0.03%) to 98.253% when pulling 14677f6 on adhikasp:modular into 459f5f5 on myint:master.

[myint]

I'm not sure I want to add the --keep-useless-pass option. autoflake currently depends on temporarily replacing unused imports/variables with pass and then removing the useless ones in a second pass. This option would result in things like the following, where we end up leaving the code in a bit of a mess.

--- original/foo.py
+++ fixed/foo.py
@@ -1,3 +1,3 @@
 def foo():
-    x = 1
-    y = 2
+    pass
+    pass

I think to properly supporting this might involve significant restructuring of autoflake. Currently, I'm fine with supporting the 99% use case where we happen to remove useless pass statements. Though, if someone came up with an elegant solution to this, I'd be fine with that as well.

[adhikasp]

Yes I agree this could make the resulting code clutters and the approach in this PR is too straightforward. I will close it in the meantime.