fix file: xhttp.h/xthread.h/xtimer.h
Merge pull request #19 from guangbin79/fix_system_api

fix file: xhttp.h/xthread.h/xtimer.h
add xthread/xhttp/xlongjmp
Merge pull request #20 from guangbin79/xthread

add xthread/xhttp/xlongjmp
add api: xtime/xdebug/xfile
Merge pull request #17 from caiywHub/feature_1

add api: xtime/xdebug/xfile，缺少xtime的部分实现
fix xC.pro/xdebug/xfile
Merge pull request #22 from guangbin79/fix_api

fix xC.pro/xdebug/xfile
fix compile warnings
Merge pull request #23 from guangbin79/fix_api

fix compile warnings
add api xmemory/ximage/xtimer