setup: Declare dependencies for nbpy2017 importer.

setup.py

@@ -1,7 +1,23 @@
 #!/usr/bin/env python3
 
+import itertools
+
 from setuptools import setup, find_packages
 
+REQUIREMENTS = {
+    'install_requires': ['babel'],
+    'setup_requires': ['pytest-runner'],
+    'extras_require': {
+        'nbpy2017': ['beautifulsoup4', 'html5lib'],
+    },
+}
+
+REQUIREMENTS['tests_require'] = [
+    'pytest',
+    'PyYAML',
+    *itertools.chain(*REQUIREMENTS['extras_require'].values()),
+]
+
 setup(
     name='import2ledger',
     description="Import different sources of financial data to Ledger",
@@ -10,12 +26,10 @@ setup(
     author_email='brettcsmith@brettcsmith.org',
     license='GNU AGPLv3+',
 
-    install_requires=['babel'],
-    setup_requires=['pytest-runner'],
-    tests_require=['pytest', 'PyYAML'],
-
     packages=find_packages(include=['import2ledger', 'import2ledger.*']),
     entry_points={
         'console_scripts': ['import2ledger = import2ledger.__main__:main'],
     },
+
+    **REQUIREMENTS,
 )