Merge pull request #87 from grissiom/static-usbd

Static usbd
Merge branch 'master' of https://github.com/RT-Thread/rt-thread into ForPullRequest
add missing dfs_mkfs prototype in dfs_fs.h
add usb state
add library file for Keil MDK project generation
Merge pull request #91 from aozima/pulls

Pulls
Merge pull request #89 from grissiom/dfs-misc-fix

add missing dfs_mkfs prototype in dfs_fs.h
Merge pull request #90 from heyuanjie87/ForPullRequest

For pull request