C++11 wrapper of state-threads library

state-threads library is a network preferred co-routines library, it is written in C, in here a C++11 wrapper is offered, to simply working with morder C++.

the project is proposed to run under Linux.

make sure the compiled state-threads library lib/include files are placed in folder st.

to run the test, gtest is required.

to build the library and test, just:

1. create a folder named build in the project root directory.
   
2. change to the directory build.
   
3. run cmake .. && make
   

typical usage:

stcpp::JoinableThread*  threads[COUNT_LOOP];
for(int i = 0; i < COUNT_LOOP; i++){
    threads[i] = new stcpp::JoinableThread(
        [](int a ) {
            stcpp::Thread::usleep(1);
            somework();
            count++;
            stcpp::Thread::exit();
        }, 100 );
}

for(int i = 0; i < COUNT_LOOP; i++){
    threads[i]->join();
}