36 add parser rule for if

[Servostar]

Added rules for branches. A branch (if) is an if <expr> {} followed by a variable amount of else if <expr> and an ended by an optional else. Valid combinations are:

if 5 {
}

if 5 {
} else {}

if 5 {
} else if 7 {}
else if 9 {}
else if 12 {}
else {}