Wrong version in the 1.6.0 release

The file stlab/version.hpp states
~~~
#define STLAB_VERSION 100506
[...]
#define STLAB_LIB_VERSION "1_5_6"
~~~

The file CMakeLists.txt also indicates the 1.5.6 version.

This makes CMake refuse the instruction
~~~
find_package(stlab 1.6.0 REQUIRED)
~~~
in my own project's CMakeLists.txt file.