Cmake fails on enabling Python bindings building

[profitware]

Hi, @Aversiste and @chipot !

Building command:

$ cmake . -DENABLE_PYTHON=ON -DBoost_DEBUG=1

produces the following output even with Boost and Python36 / 37 libraries and sources installed:

<skipped>
-- Could NOT find Boost
Boost version: 1.66.0
Boost include path: /usr/include
Could not find the following Boost libraries:
        boost_python36
Some (but not all) of the required Boost libraries were found. You may need to install these additional Boost libraries. Alternatively, set BOOST_LIBRARYDIR to the directory containing Boost libraries or BOOST_ROOT to the location of Boost.
-- Configuring done
-- Generating done
-- Build files have been written to: <skipped>

The root cause is that boost_python3 should be used instead of boost_python36 - checked this on latest Fedora and Ubuntu.

I may send pull-request fixing that behaviour along with Python packaging boilerplate or make two separate PRs.

Thanks.