Make ErrorCode a plain object, not IntEnum
Make ErrorCode a plain object, not IntEnum

Something surprising is that Python enums are really slow. In
Python 3.4, member lookup was 20x slower than normal class
attributes (https://bugs.python.org/issue23486), and even though
it has been "fixed" in subsequent Python versions, it's still
significantly slower. I don't see any reason why ErrorCode needs
to be an enum, so we can get a surprising performance improvement
for higher particle counts by changing a normal class.
OceanPARCELS/parcels,OceanPARCELS/parcels