Check file progress

[gtoonstra]

File progress is now calculated on a simple method that adds the number of bytes read from a line (len( x )) to a 'pos' attribute. It should use "tell()" instead, because when compression gets added the first summator won't be accurate (after decompression, the file moved less than indicated). The write classes are based on the readers too, so not necessary to update those.
There may be cases where the "tell()" function is not available because the file is hidden by the library (XML, HTML readers). Those cases should be investigated.