Change: Allow empty quoted identifier.

Cleanups:
- Add " to Q-CHAR
- Unify Q-IDENT variants
Closes modelica#2612

chapters/lexicalstructure.tex

@@ -89,10 +89,10 @@ \subsection{Identifiers}\doublelabel{identifiers}
 
 \begin{lstlisting}[language=grammar,mathescape=false]
 IDENT   = NONDIGIT { DIGIT | NONDIGIT } | Q-IDENT
-Q-IDENT = "'" { Q-CHAR | S-ESCAPE | """ } "'"
+Q-IDENT = "'" { Q-CHAR | S-ESCAPE } "'"
 NONDIGIT = "_" | letters "a" ... "z" | letters "A" ... "Z"
 DIGIT    = 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9
-Q-CHAR = NONDIGIT | DIGIT | "!" | "#" | "$" | "%" | "&" | "(" | ")" | "*" | "+" | "," | "-" | "." | "/" | ":" | ";" | "<" | ">" | "=" | "?" | "@" | "[" | "]" | "^" | "{" | "}"  | "|" | "~" | " "
+Q-CHAR = NONDIGIT | DIGIT | "!" | "#" | "$" | "%" | "&" | "(" | ")" | "*" | "+" | "," | "-" | "." | "/" | ":" | ";" | "<" | ">" | "=" | "?" | "@" | "[" | "]" | "^" | "{" | "}"  | "|" | "~" | " " | """
 S-ESCAPE = "\'" | "\"" | "\?" | "\\" | "\a" | "\b" | "\f" | "\n" | "\r" | "\t" | "\v"
 \end{lstlisting}
 

chapters/syntax.tex

@@ -14,13 +14,13 @@ \section{Lexical conventions}\doublelabel{lexical-conventions}
 of other lexical units):
 \begin{lstlisting}[language=grammar,mathescape=false]
 IDENT = NONDIGIT { DIGIT | NONDIGIT } | Q-IDENT
-Q-IDENT = "'" ( Q-CHAR | S-ESCAPE ) { Q-CHAR | S-ESCAPE | """ } "'"
+Q-IDENT = "'" { Q-CHAR | S-ESCAPE } "'"
 NONDIGIT = "_" | letters "a" to "z" | letters "A" to "Z"
 STRING = """ { S-CHAR | S-ESCAPE } """
 S-CHAR = see below
 Q-CHAR = NONDIGIT | DIGIT | "!" | "#" | "$" | "%" | "&" | "(" | ")" | "*" | "+" | "," |
          "-" | "." | "/" | ":" | ";" | "<" | ">" | "=" | "?" | "@" | "[" | "]" | "^" |
-        "{" | "}" | "|" | "~" | " "
+        "{" | "}" | "|" | "~" | " " | """
 S-ESCAPE = "\'" | "\"" | "\?" | "\\" |
          "\a" | "\b" | "\f" | "\n" | "\r" | "\t" | "\v"
 DIGIT = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9"