Some special characters in ids; new demos

Adds support for several special characters in identifiers. Adds a demo
for converting values to source code and another for checking equality.
Updates the existing demo and tests to reflect new names for functions
returning booleans.

src/Lexer.hs

@@ -18,7 +18,10 @@ keywordT = string "t" *> notFollowedBy alphaNumChar *> pure LKeywordT
 identifier :: Lexer LToken
 identifier = do
   first <- letterChar <|> char '_'
-  rest <- many (letterChar <|> char '_' <|> char '-' <|> digitChar)
+  rest  <- many $ letterChar 
+              <|> digitChar 
+              <|> char '_' <|> char '-' <|> char '?' <|> char '!'
+              <|> char '$' <|> char '#' <|> char '@' <|> char '%'
   let name = first : rest
   if (name == "t" || name == "__result")
     then fail "Keywords (`t`, `__result`) cannot be used as an identifier"