Add addMetalink API function
Don't exit on error in option_processing

Still it exits when -v or -h is given. They are now guarded by
standalone variable and only do so when it is true.
Don't enter daemon mode if standalone is false
Fix empty unknown option name in OptionParser::parse
Suppress console log output for library use, enclose Platform in try-catch

Still need to suppress global::cerr and global::cout
Suppress console output for none-standalone mode
Receive reference, not copy
Fix event polling not working with no downloads but keepRunning_ is true