NFD

The precompiled header core/common.hpp is used only for translation units in core/ (basically only network.cpp since version.cpp doesn't need any include). This makes the PCH feature almost useless. The bulk of NFD's code is in daemon/ and that's where the PCH should be applied.

Moreover, it would be beneficial to precompile a few additional headers on top of core/common.hpp, such as ndn-cxx/util/logger.hpp which turned out to be one of the slowest to compile due to lots of transitive Boost includes.