[examples] hello_world.c first pass; parse check touch ups; API touch ups

examples/metaprograms/hello_world.c

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+/* 
+** Example: hello world
+**
+ ** 
+**
+*/
+
+//~ Includes and globals //////////////////////////////////////////////////////
+
+// @notes Metadesk is a source-include library. So we include the
+//  file "md.c" into the usage code directly. The library 
+
+#include "md.h"
+#include "md.c"
+
+// @notes For simple single-threaded memory management in a run-once-and-exit
+//  utility, a single global arena is our prefered setup.
+static MD_Arena *arena = 0;
+
+//~ main //////////////////////////////////////////////////////////////////////
+
+int
+main(int argc, char **argv){
+    // setup the global arena
+    // @notes Metadesk arenas do linear reserve-and-commit allocation. This
+    //  code makes an arena with a 1 terabyte reserve which works so long as
+    //  we're only doing one or a few arenas.
+    arena = MD_ArenaAlloc(1ull << 40);
+    
+    // parse a string
+    MD_String8 name = MD_S8Lit("<name>");
+    MD_String8 hello_world = MD_S8Lit("hello world");
+    MD_ParseResult parse = MD_ParseWholeString(arena, hello_world_name, hello_world);
+    
+    // print the results
+    MD_PrintDebugDumpFromNode(stdout, parse.node, MD_GenerateFlags_All);
+}