Extracting and saving corrupted lines in the header

[castelao]

@OlyDLG raised some good points at #12, and we should extract and save corrupted lines, like blank lines and incomplete lines. The data section would also need something equivalent, but that's a different problem (#33) and will be in a different issue.

One idea is to save those lines into a dictionary, and include this dictionary in the header of the cnv file, i.e. the parsed object.