Add abs() for int, float and long.

[JayNakrani]

For bool, it's already supported. This produces,

$ cat build/src/haha/haha.py 
# int
haha = -42
print dir(haha)
print abs(haha)

print abs(9223372036854775807)

# float
hihi = -10.546
print dir(hihi)
print abs(hihi)

# bool
hehe = True
print dir(hehe)
print abs(hehe)

# long
huhu = long(-42)
print dir(huhu)
print abs(huhu)

$ go build haha

$ ./haha 
['__abs__', '__add__', '__and__', '__class__', '__delattr__', '__dict__', '__div__', '__eq__', '__float__', '__ge__', '__getattribute__', '__getnewargs__', '__gt__', '__hash__', '__index__', '__int__', '__invert__', '__le__', '__long__', '__lshift__', '__lt__', '__mod__', '__module__', '__mul__', '__ne__', '__new__', '__nonzero__', '__or__', '__radd__', '__rand__', '__rdiv__', '__reduce__', '__reduce_ex__', '__repr__', '__rlshift__', '__rmod__', '__rmul__', '__ror__', '__rrshift__', '__rshift__', '__rsub__', '__rxor__', '__setattr__', '__sub__', '__xor__']
42
-9223372036854775808
['__abs__', '__add__', '__class__', '__delattr__', '__dict__', '__div__', '__eq__', '__float__', '__ge__', '__getattribute__', '__getnewargs__', '__gt__', '__hash__', '__int__', '__le__', '__long__', '__lt__', '__mod__', '__module__', '__mul__', '__ne__', '__new__', '__nonzero__', '__radd__', '__rdiv__', '__reduce__', '__reduce_ex__', '__repr__', '__rmod__', '__rmul__', '__rsub__', '__setattr__', '__sub__']
10.546
['__abs__', '__add__', '__and__', '__class__', '__delattr__', '__dict__', '__div__', '__eq__', '__float__', '__ge__', '__getattribute__', '__getnewargs__', '__gt__', '__hash__', '__index__', '__int__', '__invert__', '__le__', '__long__', '__lshift__', '__lt__', '__mod__', '__module__', '__mul__', '__ne__', '__new__', '__nonzero__', '__or__', '__radd__', '__rand__', '__rdiv__', '__reduce__', '__reduce_ex__', '__repr__', '__rlshift__', '__rmod__', '__rmul__', '__ror__', '__rrshift__', '__rshift__', '__rsub__', '__rxor__', '__setattr__', '__sub__', '__xor__']
1
['__abs__', '__add__', '__and__', '__class__', '__delattr__', '__dict__', '__div__', '__eq__', '__float__', '__ge__', '__getattribute__', '__getnewargs__', '__gt__', '__hash__', '__index__', '__int__', '__invert__', '__le__', '__long__', '__lshift__', '__lt__', '__mod__', '__module__', '__mul__', '__ne__', '__new__', '__nonzero__', '__or__', '__radd__', '__rand__', '__rdiv__', '__reduce__', '__reduce_ex__', '__repr__', '__rlshift__', '__rmod__', '__rmul__', '__ror__', '__rrshift__', '__rshift__', '__rsub__', '__rxor__', '__setattr__', '__str__', '__sub__', '__xor__']
42

TestFoo fails but it is failing on master too.

Known limitation: abs(MaxInt) overflows on some platform because in Go, int(veryLargeFloat64) overflows. I've a todo for myself to figure out a safe way to handle them. Hopefully we can figure it out during code-review.

[trotterdylan]

Thanks for the PR! Unfortunately there's already a work in progress PR that implements the same functionality: #28

If you wouldn't mind reviewing that request, I would appreciate having a second set of eyes on it.

[JayNakrani]

Oh, didn't notice it there.