clean code
vcom: update device descriptor
vcom: clean descriptor for virtual com
vcom: add CDC descriptor <part1>
vcom: add CDC descriptor <part2: ep desc>
vcom: add CDC descriptor <part3>
vcom: add vcom driver inf for windows

from http://wenku.baidu.com/view/479ca22e4b73f242336c5fe2.html
support win7-64
vcom: modify inf to suit current device desc
vcom: support cdc response
fix dumphex output
vcom: close some log for performance

or uart-assistant(run on win7) will be stuck when opening the uart