README: clarify how to upgrade PETSc if necessary
Ignore PEP8 E265 (enforces blank after # in comment)
Sanitise for tougher pep8 1.5 rules
fix jacobians for extruded interval cells
Merge pull request #341 from OP2/origin/jacobian_fix

Fix Jacobian computations for extruded quads.
Create directory for code dumps if it does not exist
Fix dumping generated code for device backends
Make symbol rank optional.
Support -=, --, *=, /=, and implict casting to Symbol
None is not iterable
Fix cases in which children were not nodes.
working FunCall
Make semicolon handling for incr and decr consistent.

I am not convinced this is the Right Thing. It comes down to the statement/expression duality in C.
Make For a bit smarter about its payload