Vendor raptor source files (was embedded gitlink)

Tree vendored at upstream 0019c5dd; origin + license recorded in
raptor/VENDOR.txt. Windows SDL dev packages excluded via .gitignore.

raptor/src/m_misc.h

@@ -0,0 +1,5 @@
+#pragma once
+bool M_StringCopy(char *dest, const char *src, size_t dest_size);
+bool M_StringConcat(char *dest, const char *src, size_t dest_size);
+char *M_StringJoin(const char *s, ...);
+int M_snprintf(char *buf, size_t buf_len, const char *s, ...);