remove RT_LWIP_TCP_SND_BUF setting

When not configured in rtconfig.h, lwipopt.h will give us a reasonable
value(TCP_MSS * 2).

rm48x50: restore missing include for __TI_COMPILER_VERSION__

Please @Grissiom check why add this header file in rtthread.h.

convert the Tabs to Spaces

convert Tabs to spaces

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.

update libcpu/arm/cortex-m4: support lazy stack optimized.