Add adapters/libhv

[ithewei]

Build steps:

git clone https://github.com/ithewei/libhv
cd libhv
./configure && make && sudo make install

git clone -b libhv https://github.com/ithewei/hiredis
cd hiredis
mkdir build
cd build
cmake .. -DENABLE_EXAMPLES=ON
make
./examples/example-libhv

output:

Connected...
argv[end-1]: ./examples/example-libhv
Disconnected...