add compiletimeassert.h

CHANGES

@@ -1,3 +1,6 @@
+0.30:
+  add compiletimeassert.h
+
 0.29:
   save 8 bytes in taia.h for 64-bit systems
   add buffer_tosa (buffer writing to auto-growing stralloc)

compiletimeassert.h

@@ -0,0 +1,4 @@
+
+#define __X(x, y) x ## y
+#define __Y(x, y) __X(x, y)
+#define compiletimeassert(cond) struct __Y(foo,__LINE__) { char __temp[1 - (!(cond))*2]; };