I've extended support of Nikon maker note in the "Olympus" part,

I've extended support of Nikon maker note in the "Olympus" part,
where Lutz originally put the first code.
It appears there are at least 3 versions of Nikon mnote:
1) IFD with 0x1B items - was confused w/ Pentax-made mnote
2) 'Nikon',0,1,0,IFD
3) 'Nikon',0,2,0,0,0, 8-byte TIFF header, IFD

In addition to that, there are 2 sets of tags:
a) 'Version 1' is used by cases 1)+2)
b) 'Version 2' is used by case 3)
A bad thing is that both sets use the same ids.
Furthermore, while v1 uses SHORT values, v2 uses ASCII values
containing the actual string representations of the numeric values.
To distinguish v1 & v2 tags, MNOTE_NIKON1_TAG_BASE (0x8000)
is added to every tag if reading a v1 file - this is done in
exif_mnote_data_olympus_load().
Some of the tags are explained here:
http://park2.wakwak.com/~tsuruzoh/Computer/Digicams/exif-e.html
most of other tags are work (?) of Serge Droz <serge.droz@psi.ch>
who submitted the original code enhancing now obsolete libmnote.
Meaning of many tags remains unknown.