Open curved-edge-support branch
Add attributes about edge-radius.

 * `edge_radius` for diagram
 * `radius` for edge
Imprement curved edge.
Fix for PEP8 compliance
Apply trivial fixes to conform with pep8.

`not parent in circular` is replaced with the equivalent, preferred
`parent not in circular`

Also a line of dead code is removed.

Resolves the following
complaints:

py27 runtests: commands[2] | flake8 src
src/blockdiag/builder.py:242:28: E713 test for membership should be 'not in'
src/blockdiag/tests/test_pep8.py:46:9: E265 block comment should start with '# '
Merge remote-tracking branch 'iwata0303/branches/curved-edge-support' into merge-curved-edge-support

Conflicts:
	src/blockdiag/drawer.py
Merge branch 'pep8-fixes'