* Replaced push_back calls with emplace_back where applicable.
* Replaced size() == 0 and size() != 0 with empty() and !empty().
* Replaced C style loops for range for loops where applicable.
* Fixed mismatching arg names between function declarations and definitions.
* Replaced NULL and 0 (in the context of pointers) with nullptr.
* Remove unnecessary calls to string::c_str() where applicable.
* Replaced deprecated C headers with proper C++ headers.
* Removed unnecessary null pointer checks when deleting pointers
(deleting a null pointer has no effect).
* Fixed a potential memory leak in apngloader.cpp file.
* Replaced unsafe strcpy with strncpy in the demangle_name function.
