controlspeed 1.0

# ControlSpeed
这项目是用来控制函数调用的频率

#Usage:

装饰器使用方法
```
from controlspeed import ControlSpeed
@ControlSpeed(max_calls=10, period=1.0)
def do_something():
pass
```

with关键词控制上下文
```
from controlspeed import ControlSpeed
rate = ControlSpeed(max_calls=10, period=1.0)
for i in range(100):
with rate:
do_something()
```

支持回调函数的控速
```
from controlspeed import ControlSpeed
import time
def limited(until):
duration = int(round(until - time.time()))
print 'Speed limited, sleeping for %d seconds' % duration

rate = ControlSpeed(max_calls=2, period=3, callback=limited)
for i in range(3):
with rate:
print i
```