Expressions

- Support and documentation for rc.patterns, which enables/disables
  support for /pattern/ command line arguments.
- Support and documentation for rc.expressions, which enables/disables
  support for command line expressions.
- Now canonicalizes attribute names.
- Now canonicalizes modifier names.
- New colorization (temporary) that colors all Arguments::dump output
  green when processed.
- New distinction between 'old' and 'new' style command lines.  Old style
  is "pro:A +foo pri.not:M" with implicit "and" operators.  New style
  includes operators but does not include "+foo" and "/foo/".
- Many tokens are converted directly to primitive types (int, number,
  string) when no further processing is required.
- Restored CmdShow to functionality, and linearized the list of supported
  configuration variables, for easier insertion.
- Modified arguments.t.cpp unit tests.

src/Expression.h

@@ -49,8 +49,11 @@ private:
   void expand_attmod ();
   void expand_word ();
   void expand_expression ();
+  void expand_tokens ();
   void postfix ();
 
+  bool is_new_style ();
+
 private:
   Arguments _args;
 };