Improve README.md and print used options during compilation

README.md

@@ -9,6 +9,9 @@ Compilation
 
 Just do `make`. Requires Cython >= 0.17.
 
+To compile with nondefault options use i.e. `CXXFLAGS="-DSAVE_MEMORY=0" make`
+to turn off `SAVE_MEMORY`. For list of options see file `compileTimeOptions.h`.
+
 Usage
 -----
 

compileTimeOptions.h

@@ -5,7 +5,11 @@
 #ifndef SAVE_MEMORY
 #define SAVE_MEMORY 1
 #endif
-
+#if SAVE_MEMORY
+#pragma message "SAVE_MEMORY ON"
+#else
+#pragma message "SAVE_MEMORY off"
+#endif
 
 #endif