#28 Make index portable

The index (whether a forest file or a collection of .iod files) should be portable across platforms.
It should contain a code identifying the version of the product used.
And it should also include the text from the original file.
The scanning of the .kelp file should be made to deal with different line endings recognising nl and crnl and cr in the same file (possible due to using different editors at same time.
The iod file should possibly be compressed (option at runtime) and something will tell whether it is (possibly the extension?) like for man pages.