Restructure project, add gebs_exists() and gebs_mkdir()

example/.gitignore

@@ -1,3 +0,0 @@
-gebs
-a.out
-main

example/gebs.c

@@ -1,13 +0,0 @@
-#define GEBS_IMPLEMENTATION
-#include "../gebs.h"
-
-int main(int argc, char ** argv)
-{
-    gebs_rebuild_self(argc, argv, "cc", "-o", "gebs", __FILE__);
-
-    if (GEBS_CMD("gcc", "-o", "main", "main.c") != 0) {
-        return 1;
-    }
-    
-    return 0;
-}

example/main.c

@@ -1,7 +0,0 @@
-#include <stdio.h>
-
-int main(void)
-{
-    printf("Hello world\n");
-    return 0;
-}

example/self_rebuild.c

@@ -0,0 +1,11 @@
+#include <stdio.h>
+#define GEBS_IMPLEMENTATION
+#include "../gebs.h"
+
+int main(int argc, char ** argv)
+{
+    gebs_rebuild_self(argc, argv, "cc", "-o", "self_rebuild", __FILE__);
+
+    printf("Hello world\n");
+    return 0;
+}