Engineering improvements for 4.15

[gongminmin]

• [x] One unified solution
• [x] Remove clang/c2 support
• [x] Ninja building system
• [x] Windows build on Travis-ci
• [x] Using CMake + git to manage external libraries
• [x] Make zlib share between external libraries
• [x] Update external libraries
• [x] Enable to build by VS buildtools
• [x] Explore shared PCH
• [x] VS2019 support

[gongminmin]

Shared PCH doesn't speed up the build. Abandon this approach.