fixed the string descriptor send to host more than actual

more deterministic on timer

If two timer will timeout at the same tick, the one started later will
be called later. I've tested the patch on simulator and it _seems_ OK.
Reported-by: xdzy on the forum and delin17 <delin17@qq.com>

handle standard request to interface that defined in class

Add RT_MTD_ESRC definitions. If the source page has issue when copying a page, the low level can return this error code. 

remove math code for newlib

libm is a frequently used lib. Newlib is compiled with
-ffunction-sections in recent GCC tool chains. The linker would just
link in the functions that have been referenced. So setting this won't
result in bigger text size.

Usb device:correct the macro

Usb-device

Newlib already have optimized and full featured math implementation. To
use it, one should add:

    env['LIBS'] = ['m']

or equivalent to the SConstruct.

fix math.h

Declare sin/cos and M_PI in math.h.

remove product ID

add a dcd operation to send status in control transfer

Correct crlf

LGTM, thanks!