fix file: xinteger.h
Merge pull request #13 from guangbin79/fix_integer

fix file: xinteger.h, merge.
api impl demo - 1
Merge pull request #15 from guangbin79/feature_http

api impl demo - 1
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