Cleanup version handling slightly (#149)

Some improvements I saw over on
https://github.com/FactoryBoy/factory_boy/pull/676/files that looked
useful here as well.

docs/conf.py

@@ -17,6 +17,8 @@ import pkg_resources
 import sys
 import time
 
+import flask_debugtoolbar
+
 
 BUILD_DATE = datetime.datetime.utcfromtimestamp(int(os.environ.get('SOURCE_DATE_EPOCH', time.time())))
 
@@ -56,16 +58,10 @@ copyright = u'2012-{0}'.format(BUILD_DATE.year)
 # The version info for the project you're documenting, acts as replacement for
 # |version| and |release|, also used in various other places throughout the
 # built documents.
-try:
-    release = pkg_resources.get_distribution('Flask-DebugToolbar').version
-except pkg_resources.DistributionNotFound:
-    print('Flask-DebugToolbar must be installed to build the documentation.')
-    print('Install from source using `pip install -e .` in a virtualenv.')
-    sys.exit(1)
-
-if 'dev' in release:
-    release = ''.join(release.partition('dev')[:2])
-
+#
+# The full version, including alpha/beta/rc tags.
+release = flask_debugtoolbar.__version__
+# The short X.Y version.
 version = '.'.join(release.split('.')[:2])
 
 # The language for content autogenerated by Sphinx. Refer to documentation