Revendor editor and make dateutil optional

Re-implemented the ``python-editor`` dependency as a small internal
function to avoid the need for external dependencies.
The implementation is based on the original
version in 7b91b325ff43a0e9235e0f15b57391fa92352626.

Make the ``python-dateutil`` library an optional dependency.
This library is only required if the ``timezone`` option
is used in the Alembic configuration.
An extra require named ``tz`` is available with
``pip install alembic[tz]`` to install it.

Fixes: #674
Fixes: #856
Change-Id: I07f17b2fea01e3a3d677ce95333fe3e8d8d438fd

1 files changed, 3 insertions, 1 deletions

diff --git a/setup.cfg b/setup.cfg
index 59be536..b168de5 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -44,7 +44,9 @@ python_requires = >=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*, !=3.4.*, !=3.5.*
 install_requires =
     SQLAlchemy>=1.3.0
     Mako
-    python-editor>=0.3
+
+[options.extras_require]
+tz =
     python-dateutil
 
 [options.packages.find]