add meson.build

[shenlebantongying]

Related https://github.com/mikehaertel/minrx/issues/10

Meson by default follows typical conventions of GNU systems, so only a few lines of code is needed to meet “modern expectations”.

Basic usages:

meson setup buildDir --prefix=/user/local/ --buildtype=release

cd ./buildDir 

meson compile (or ninja)

meson install (or ninja install)

ninja uninstall

Under the prefix, these file would be installed.

.
├── include
│   └── minrx.h
├── lib
│   ├── libminrx.0.dylib
│   ├── libminrx.dylib -> libminrx.0.dylib
│   └── pkgconfig
│       └── minrx.pc
└── share
    └── man
        └── man3
            └── minrx.3

For consuming the library, the generated pkgconifg file should meet the “modern expectations” as all C/C++ build systems supports it.

:)