Merge pull request #88 from grissiom/fix-sim-serial

simulator: fix serial_write
make Host can halt endpoints
Merge pull request #93 from heyuanjie87/ForPullRequest

For pull request
cdc_vcom: reset the vcom state in proper cases

Reset the vcom state in class_{run,stop} and when the PC is not
receiving data from me.
Merge pull request #94 from grissiom/vcom

cdc_vcom: reset the vcom state in proper cases
usbdevice/core: add reset function to support hotplug

When the USB got RESET packet from the host and the address is setup,
all the classes will got reset. The reset is done by class stop and than
class run. So the classes should reset their internal state in
class_{run,stop}.

Besides, the USB device driver could post a USB_MSG_RESET message on
every RESET packet.
Merge pull request #95 from grissiom/vcom

usbdevice/core: add reset function to support hotplug