masm/bnf-grammar: Format some literal characters correctly (#4456)

A couple of character literal terminals don't follow consistent
formatting. Fix that.

Author: lkundrak

docs/assembler/masm/masm-bnf-grammar.md

@@ -22,7 +22,7 @@ The BNF grammar allows recursive definitions. For example, the grammar uses *`qu
   *`endOfLine`* | *`comment`*
 
 *`=Dir`*\
-  *`id`* = *`immExpr`* *`;;`*
+  *`id`* **`=`** *`immExpr`* *`;;`*
 
 *`addOp`*\
   **`+`** | **`-`**
@@ -492,7 +492,7 @@ The BNF grammar allows recursive definitions. For example, the grammar uses *`qu
   *`immExpr`*\
   | *`string`*\
   | **`?`**\
-  | *`constExpr`* **`DUP`** ( *`scalarInstList`* )\
+  | *`constExpr`* **`DUP`** **`(`** *`scalarInstList`* **`)`**\
   | *`floatNumber`*\
   | *`bcdConst`*
 
@@ -591,7 +591,7 @@ The BNF grammar allows recursive definitions. For example, the grammar uses *`qu
 
 *`macroCall`*\
   *`id`* *`macroArgList`* *`;;`*\
-  | *`id`* ( *`macroArgList`* )
+  | *`id`* **`(`** *`macroArgList`* **`)`**
 
 *`macroDir`*\
   *`id`* **`MACRO`** ⟦ *`macroParmList`* ⟧ *`;;`*\
@@ -716,7 +716,7 @@ The BNF grammar allows recursive definitions. For example, the grammar uses *`qu
   | **`OLDMACROS`** | **`NOOLDMACROS`**\
   | **`OLDSTRUCTS`** | **`NOOLDSTRUCTS`**\
   | **`PROC`** **`:`** *`oVisibility`*\
-  | **`PROLOGUE`** : *`macroId`*\
+  | **`PROLOGUE`** **`:`** *`macroId`*\
   | **`READONLY`** | **`NOREADONLY`**\
   | **`SCOPED`** | **`NOSCOPED`**\
   | **`SEGMENT`** **`:`** *`segSize`*\