More user-friendly code needed

[jubiiz]

The code has a number of user-unfriendly features that would benefit to be altered.
These features need to be corrected before issue #13 can be tackled.
Here is a brief list of what they are:

• multiple changes of filename required per source-file
• inconsistent filename input (sometimes it's "filename.txt", others just "filename")
• unclear and inconsistent data size input (a few files still rely on the fact that the problem will be 20x20, and do not have a centralized way of changing those numbers)