[kernel]修改定时器 hook 函数

修复syslog.c缺少#include <sys/time.h>

[kernel]Change 'rt_timer_timeout_hook' function to 'rt_timer_enter_hook' and add 'rt_timer_exit_hook' hook function.

原因tm = gmtime_r(&now, &tm_tmp);报错

原因 tm = gmtime_r(&now, &tm_tmp);报错

[net][at] Modify AT CLI configuration

修复scons --target=vsc 不支持py3的问题

[Tools] Fix the RTT_ROOT issue

[Kernel] Add ARCH_CPU_STACK_GROWS_UPWARD option

[BSP] remove settings folder in stm32f411-nucleo

[Tools] Change building script for Py3

[libc] Fix the _EXFUN issue in newlib

Update travis-ci setting.

[component][ulog] Fix a input parameter check error.

Fix kconfig

[bsp]fixed drv_usart.c because f411xE have no USART3

Fix ulog

Remove gdbstub

[BSP][ls1c] fix config issue

Update .gitignore

Untrack cscope and ctags files.