added new directory interpret++

recursiveDescentParsers/cplusplus/README.md

@@ -15,13 +15,24 @@ There are (or will be some day) subdirectories here:
      This code take mathematical expressions and evaluates them,
      i.e. it outputs numbers.
      
-  2. `halfBakedCompiler`  
+  1. `interpreter++`  
+     This code does exactly what interpreter does 
+     (except for `make test`, which does more). 
+     The major difference is more extensive use of C++ features, 
+     including the new (C++17) `std::variant<>` template. 
+     Testing is also more extensive.
+     This is meant mostly as a preparation for larger projects where
+     software engineering aspects becomes more important 
+     whereas the version in `interpreter` (see above) is meant
+     to get down to recursive descent parsing as quickly as possible.
+     
+  1. `halfBakedCompiler`  
      This code takes mathematical expressions and convets them into
      an AST (Abstract Syntax Tree), then dumps that tree to output
      (i.e. displays the tree as text).  It does nothing really useful,
      in other words.
      
-  3. `LLVMcompiler`  
+  1. `LLVMcompiler`  
      This is vaporware -- in other words, it does not exist yet, and
      may never do so. But I hope someday to create a version that 
      builds the AST, then converts it to LLVM IR, and then evaluates