Memory leak fixes and code refactorization

[radomik]

Hello, I've created improved version of my previous pull request #17.

Now I've split changes into 4 commits to improve readability as You wanted (it was not too hard but allowed also for me to easier track the changes).

New error messages are reduced to absolute minimum (mainly connected with fread errors which should almost never occur).

Best regards, Dariusz Mikołajczuk