Add parallel support for large compressed zip members

[mxmlnkn]

This goes in the same direction as #97 and #98, i.e., more and more in-house processing of zip archives in order to improve performance. See also the discussion in #104 about performance.

It should be possible to use the StenciledFile file class on the actual member data of the zip archive and give it to pragzip or indexed_bzip2 or indexed_gzip depending on the compression. Note that deflate is the most common and best-supported zip compression format. However, this requires the gzip backend to work with a raw deflate stream instead of a gzip file. These are small rough corners but it wouldn't work out of the box because of that.

[mxmlnkn]

A possible use case for this is mentioned here:

pauldmccarthy/indexed_gzip#109
https://github.com/forrestfwilliams/index_safe