add logtrace component

Logtrace is a component that could output the log into either a device
or a file. It has the ability to filter the log messages according to a
pre-module level. Define RT_USING_LOGTRACE in rtconfig.h if you want to
have a try.
Merge pull request #113 from grissiom/logtrace

add logtrace component
Embedded GPLv2 license in dfs
Embedded GPLv2 license in pthreads
Embedded GPLv2 license in components
Embedded GPLv2 license in drivers
additional update
reformat the coding style

convert Tabs to spaces
reformat the coding style in usbdevice/core/core.c
reformat the coding style in dfs_ramfs.c
reformat the coding style in rtdef.h

convert the Tabs to Spaces
reformat the coding style in rthw.h