add lwip 1.4.1 source code
fix math.h

Declare sin/cos and M_PI in math.h.
Merge pull request #10 from grissiom/fix-math

fix math.h
Merge pull request #9 from heyuanjie87/usb-device

Usb-device
Merge pull request #12 from heyuanjie87/usb-device

Usb device:correct the macro