Since this change, the libosmogapk uses the Osmocom logging
framework. By default, logging is disabled and could be enabled
by the external applications calling the osmo_gapk_log_init()
with a desired log target as an argument.
There is no need to expose the implementation details of both
BENCHMARK_START and BENCHMARK_STOP macros via public header.
This change moves them to a separate private header 'bench.h'.
To be able to use the library, external applications need to know,
which symbols are exposed. This information is provided by header
files, which are being installed to a system's ${includedir}
since this change.
Vadim Yanitskiy
Sylvain Munaut