jcrocholl/pep8 (used by flake8, used in Hy's continuous integration
builds) introduced an imports-at-top-of-file check in 1.6.0 and a
line-breaks-around-binary-operators check in 1.6.2. This commit makes
nonfunctional changes to bring the Hy codebase in compliance with this
tool, fixing #764.
A macro is available in the module where it was defined and
in any module that does a require of the defining module.
Only macros defined in hy.core are globally available.
Fixes#181
