Prevent -mno-fused-madd issue in build

[dhermes]

Prevent -mno-fused-madd issue in the build step either by setting

export CFLAGS=-Qunused-arguments
export CPPFLAGS=-Qunused-arguments

in the environment called by setup.py or simply document the workaround on OS X.

NOTE: Opened as an unfinished item from #7

[dhermes]

Potentially useful code:

>>> import platform
>>> platform.dist()
('Ubuntu', '12.04', 'precise')
>>> platform.mac_ver()
('', ('', '', ''), '')