README: add C# info. Cleanup top Makefile.

Also, re-order impls into alphabetical order.

README.md

@@ -3,18 +3,19 @@
 ## Description
 
 Mal is an interpreter for a subset of the Clojure programming
-language. Mal is implemetated from scratch in 10 different languages:
+language. Mal is implemetated from scratch in 11 different languages:
 
-* Javascript
-* Python
-* Clojure
-* C
-* Java
-* PHP
 * Bash shell
+* C
+* C#
+* Clojure
+* Java
+* Javascript
 * GNU Make
 * mal itself
-* Postscript (in-progress)
+* PHP
+* Postscript
+* Python
 
 
 Mal is also a learning tool. Each implentation of mal is separated
@@ -62,6 +63,19 @@ make
 ./stepX_YYY
 ```
 
+### C#
+
+The C# implementation of mal has been tested on Linux using the Mono
+C# compiler (mcs) and the Mono runtime (version 2.10.8.1). Both are
+required to build and run the C# implementation.
+
+```
+cd cs
+make
+mono ./stepX_YYY
+```
+
+
 ### Clojure
 
 ```

cs/Makefile

@@ -1,5 +1,7 @@
 #####################
 
+DEBUG =
+
 TESTS =
 
 SOURCES = readline.cs types.cs reader.cs printer.cs env.cs core.cs \
@@ -15,7 +17,7 @@ SRCS = step0_repl.cs step1_read_print.cs step2_eval.cs step3_env.cs \
 
 LIB_SRCS = $(filter-out step%,$(OTHER_SOURCES) $(SOURCES))
 
-FLAGS = -debug+
+FLAGS = $(if $(strip $(DEBUG)),-debug+,)
 
 #####################