neither ignore_nan=True nor allow_nan=False handle Decimals correctly #149

import math
from decimal import Decimal
import numpy as np
import simplejson

fmath = [1/3, math.nan, 0.2]
fnp = np.array([1/3, np.NaN, 0.2])
dmath = [Decimal(v).quantize(Decimal('0.01')) for v in fmath]
dnp= [Decimal(v).quantize(Decimal('0.01')) for v in fnp]

print(simplejson.dumps(fmath, ignore_nan=True))
print(simplejson.dumps(fnp.tolist(), ignore_nan=True))
print(simplejson.dumps(dmath, ignore_nan=True))
print(simplejson.dumps(dnp, ignore_nan=True))