ReadCentralDir parameter

[thomas694]

Sometimes you have a large archive and only need to access one or a small number of the files. However, to get metadata you need to call ReadCentralDir which in turn calls GetFileOffset that seeks and reads twice to calculate each file offset.
This is unnecessary unless you are interested in the file offsets or want to extract files.

The new version calculates the file offset only when needed in ExtractFileAsync. This feature is only active if the optional parameter was used.