*.cmtklandmarks->*.landmarks.cmtk

* again for consistency
* expect to hide them anyway soon
Add generic write.landmarks function

* including full docs
fix some buglets in write.landmarks

* nb some other functions presently won't overwrite - need to check that.
Remove Force parameter from write.landmarks.cmtk

* will deal with this in write.landmarks
No longer export *.landmarks.cmtk
No longer export *.landmarks.amira
More examples for landmarks i/o