1) UnlockGuard is moved from gravifon_scobbler_deadbeef_plugin to libafc;
2) std::printf is used instead of ::printf;
3) a spelling mistake is corrected.
currentUTCTimeSeconds() is introduced.
UrlBuilder::paramName(const std::string &) and ::paramValue(const std::string &) are introduced.
The functionality from the C++ standard library is used accurately.
LastfmScrobbler: authentication is implemented. (contributes to #14)