docs: unify the documents about tcl parser

[masatake]

https://github.com/universal-ctags/ctags/blob/master/docs/parser-tcl.rst (the web page) should be merged to the man page for tcl parser.

Originally posted by @masatake in #3149 (comment)

---

One of the known bugs described in the web page can be fixed if we add a "langType" field to the data structure (scopeSeparator) representing scope separators.

 typedef struct sScopeSeparator {
-       int parentKindIndex;
+       /* If the value is LANG_IGNORE, any language used as parent
+          language is matched. In the other words, LANG_IGNORE is
+          wildcard.
+
+          If the value is LANG_AUTO, the field is replaced with
+          the langType of the owner of this scope separator. */
+       langType parentLang;
+       int parentKindIndexx;
        const char *separator;
 } scopeSeparator;