Conditional expresssions implemented in master

The latest practicomp now supports conditional expressions. As discussed, these should have the form:

if( condition ) {
  // The curly braces are mandatory for conditional expressions
  statement;
  statement;
  expression // No semicolon at end
} else {
  // The else clause is mandatory
  statement;
  statement;
  expression // No semicolon
}

The two expressions’ type follow the same promotion rules as for binary operators.

As discussed before, if you want to use the conditional value as part of a larger expression, the entire structure must be inside parenthesis.