Using wrong brackets: better error message 


Currently, following program

```
#ground v(1).
```

results in this error message: 
```
Fatal error: exception Invalid_argument("Parser error. In file error.bul, at line 6, column 9: syntax error. <YOUR SYNTAX ERROR MESSAGE HERE>\n (error 56)")
```

Better error message: 

Line 1, wrong usage of parenthesis for extensional atom. Please use brackets.   


