Fixes BKWLD/laravel-pug#82

Observed:
When the dot fails to know if the right operand is a field/property of the left operand, it returns an array [left, right] so it can be tried as a callable if called.

1. When this array is passed to a condition (evaluated as a boolean) it's always true even if the right operand does not match anything truthy in the left operand.
2. When it's sent to the output (evaluated as a string), it fails because PHP cannot cast arrays to string.

Expected:

1. When this array is passed to a condition (evaluated as a boolean) it's always true even if the right operand does not match anything truthy in the left operand.
2. When it's sent to the output (evaluated as a string), it fails because PHP cannot cast arrays to string.

Solution proposal:
This array should be wrapped in an object that:

• can be cast to string according to the property/field value;
• is callable as the original array would be;
• provies a __toBoolean method that other libraries (like Phug/Pug-php) could use to cast it as a boolean.