The SeekableDownloadChannel implements SeekableByteChannel and allows to
set the position of the channel and read data from that point onward.
The SeekableDownloadChannel implementation, creates a new internal
DownloadChannel at every call to position(long), that will create a
resume channel onto that point, thus, not all service implementations
are supported.
This commit creates several maven modules for each segment of the
library. Now it is possible to include only individual services to the
classpath instead of the full library.
