Resolved issue #1

This is done by splitting text strings by newlines and storing separate lines in different vectors.

*The typedef collection_type has been changed from `std::vector<sf::Text>' to `std::vector<std::vector<sf::Text> >'
+A new typedef, line_type, has been added as an alias to `std::vector<sf::Text>'
*Basically every function has been changed to accomodate the new collection_type, but the interface remains the same.