Fixed operator precedence

Placed all operators inside the `expr` rule to get the expected operator precedence.

Changed:

    expr
     : ...
     | expr binop expr
     | ...
     ;

    binop
     : '+' | '-' | AND | OR | ...
     ;

to

    expr
     : ...
     | expr ('+' | '-') expr
     | expr AND expr
     | expr OR expr
     | ...
     ;
Merge pull request #47 from bkiers/patch-1

Fixed operator precedence