Tweaked .gitignore
Expose ZipEntry.HostSystem as HostSystemID enum instead of int
Back ZipEntry.DateTime with a real DateTime field instead of DosTime

Otherwise we lose the additional accuracy we gain from Unix or NT timestamps.
Changing DateTime externally also changes DosTime. DosTime is only mapped to DateTime once on load, if there is no Unix or NT timestamp.
Improve extracting Unix and NT timestamps from ZipExtraData

Tries to match the behavior of InfoZIP's unzip as closely as possible.
Incremented version number