Release v1.9.3

The branch srs will be patched the following patches:

• ARM: Patch st.arm.patch, for ARM.
• OSX: Patch st.osx.kqueue.patch, for osx.
• Linux: Patch st.disable.examples.patch, for ubuntu.
• System: Refine TAB of code.
• ARM: Merge from michaeltalyansky and xzh3836598, support ARM.
• Valgrind: Merge from toffaletti, support valgrind for ST.
• OSX: Patch st.osx10.14.build.patch, for osx 10.14 build.
• ARM: Support macro MD_ST_NO_ASM to disable ASM, #8.
• AARCH64: Merge patch srs#1282 to support aarch64, #9.
• OSX: Support OSX for Apple Darwin, macOS, #11.
• System: Refine performance for sleep or epoll_wait(0), #17.
• System: Support utest by gtest and coverage by gcov/gocvr.
• System: Only support for Linux and Darwin. #19, srs#2188.
• System: Improve the performance of timer. 9fe8cfe5b, 7879c2b, 387cddb
• Windows: Support Windows 64bits. #20.
• MIPS: Support Linux/MIPS for OpenWRT, #21.