Refactor logging subsys using SDL2 logging facilities

* Remove NOM_DEBUG_TRACE preprocessor definition; this feature is
now controlled at run-time (see NOM_LOG_CATEGORY_TRACE).

* platforms.hpp: Rename __func__ to NOM_FUNC.

* init.cpp: Enable all logging for the default NOM category. Disable
function call traces on NOM_LOG_CATEGORY_TRACE category levels, which
does not yet have any effect, since we are still using the legacy NOM
logging category (meaning traces will be enabled for everything).

* SDL2LoggerTest: Introduce unit test for SDL2Logger

* examples/macros.cpp: Clean up file a bit
Rename log source files SDL2Logger
UIBoxLayout: Fix compile err

* This err is due to the recent refactoring of nomlib's logging
subsystem; the macro signature has changed slightly.
Fix WinFile::currentPath method

* Freeing the buffer within WinFile::currentPath led to invalidating
the memory holding the return value (path).
  This resolves the unit test failure of RenderWindowTest::SetIcon.

* Remove const keyword from ::currentPath return value (const has no
effect on pass by value)
Dog-food test clean up of SDL2Logger feature

* Remove logging category enums: NOM_LOG_CATEGORY_TRACE_GRAPHICS,
NOM_LOG_CATEGORY_TRACE_MATH.

* Add logging category enums: NOM_LOG_CATEGORY_TRACE_VIDEO,
NOM_LOG_CATEGORY_TRACE_RENDER, NOM_LOG_CATEGORY_TRACE_STATES,
NOM_LOG_CATEGORY_TRACE_SYSTEM.

* Introduce NOM_LOG_CATEGORY_CUSTOM enumeration; this lets us extend
the usage of  defining custom logging categories to applications that
use nomlib -- i.e.: TTcards.

* Use NOM_LOG_CATEGORY_TRACE_AUDIO category for function traces in
audio subsystem.

* Use NOM_LOG_CATEGORY_TRACE_RENDER category for function traces in
nom::AnimatedSprite class.

* Use NOM_LOG_CATEGORY_TRACE_SYSTEM category for function traces in
nom::SDLApp.

* Remove the explicit disabling of logging traces in nomlib from
initialization; this is un-necessary because the default priority is
already SDL_LOG_PRIORITY_CRITICAL.
Remove GameCursor class

* This interface is entirely worthless; it does nothing more than
inherit from AnimatedSprite.
Text: Fix performance bug in ::set_text

* This corrects a severe performance bug found (in TTcards) when
updating the text field every frame; this caused several needless
performance-heavy operations to be done, such as the creation
of a new texture, potential rebuilding of glyph cache and so on
by calling ::update after updating the text variable.
Remove ancient MSVCPP project files

* These were the original MSVCPP project files used for generating
nomlib's examples; a backup of the files has been made in the local
repo of nomlib inside the tmp dir. CMake has long replaced these.