style: Fix style issues and add flake8 as a requirement

Author: jcfr

castxml/__init__.py

@@ -37,4 +37,4 @@ def _program(name, args):
 
 
 def castxml():
-    raise SystemExit(_program('castxml', sys.argv[1:]))
+    raise SystemExit(_program('castxml', sys.argv[1:]))

requirements-dev.txt

@@ -1,4 +1,5 @@
 cmake
+flake8>=3.0.4
 pytest>=4.5.0
 pytest-runner>=5.1
 pytest-virtualenv>=1.7.0

setup.py

@@ -9,6 +9,7 @@
 with open('README.md', 'r') as fp:
     readme = fp.read()
 
+
 def parse_requirements(filename):
     with open(filename, 'r') as file:
         return TextFile(filename, file).readlines()
@@ -70,4 +71,4 @@ def parse_requirements(filename):
     install_requires=requirements,
     tests_require=dev_requirements,
     setup_requires=setup_requires
-    )
+    )