Added StringFormat class, which internally calls vasprintf.
operator<< is defined for this class, so it can be used with iostream
classes nicely. SimpleLogger and following functions are rewritten
using StringFormat class.
Besides, now Logger class's methods are non-const, many classes
that has a const Logger* as a member variable are modified to remove
const qualifier from the variable declaration.
* src/HelpItemFactory.cc
* src/Request.cc
* src/SimpleLogger.cc
* src/StringFormat.cc
* src/StringFormat.h
* src/Util.cc
* src/option_processing.cc
* src/version_usage.cc
* test/StringFormatTest.cc
* src/*.h: The classes that has const Logger* as a member variable.
Tatsuhiro Tsujikawa