feat(parser): macro expansion, conditionals and include splicing with -I

Assisted-by: GLM 5.3 Flash

token/token.go

@@ -43,6 +43,13 @@ const (
 	At     // @
 	Hash   // #
 	Pipe   // |
+
+	// Semicolon separates statements on one line (a Plan 9 statement
+	// terminator); Ampersand and Tilde are the expression operators & and ~
+	// of constant expressions.  All three appear mostly inside macro bodies.
+	Semicolon // ;
+	Ampersand // &
+	Tilde     // ~
 )
 
 var kindNames = map[Kind]string{
@@ -71,6 +78,10 @@ var kindNames = map[Kind]string{
 	At:      "@",
 	Hash:    "#",
 	Pipe:    "|",
+
+	Semicolon: ";",
+	Ampersand: "&",
+	Tilde:     "~",
 }
 
 // String returns a human-readable name for the kind.