Switch to Boost.Log from google-glog, and some more clean-ups

Hi,

google-glog doesn't support Android and as this project already has a strong connection to Boost, I thought why not drop the google-glog dependency and switch to Boost.Log instead, which all or most Boost users already have readily available.

It doesn't have the LOG() vs. DLOG() distinction but apart from that, the API is strikingly similar. Performance characteristics should be comparable. Both are fairly powerful and can be extended / rerouted as desired by the host application.

In order to test it, I also had to fix some more CMake issues. Hence the two other patches that are unrelated to the logger switch per se.