Various CMakeLists.txt fix to ease Debian integration.

Dear console_bridge maintainers,
this pull request integrates all the changes required to produce a Debian package following
the Debian policy from the last release.

Technically speaking:

 * make sure CMake clean the files it generates
 * rely on GNUInstallDirs.cmake to make package deployment more flexible
 * fix distributed CMake macro and pkg-config file to reflect the changes.
 * specify the SOVERSION for the generated library (please be careful to update this
  number accordingly in the next releases).