This PR tries to clarify the terminology used in landmarkLabels. It is in follow up to an email between me and the BUNPC.

First, the old text referred to probe.landmark, which does not exist. I assume this was meant to refer to probe.landmarkPos2D and probe.landmarkPos3D, so I added probe.landmarkPos to refer to both 2 and 3D.

Second, I make a change to the landmarkLabels text as I believe it conflated "landmarks" and "standardized placement systems".

Landmarks are positions on the skull that are used to guide sensor placement. E.g. Nasion, Inion, LPA, RPA
Standardized placement systems specify locations on the head to place sensors. E.g. 10-20

• Landmarks are standard points on the skull and the placement of sensors is "based on landmarks on the skull, namely the nasion (Nz), the inion (Iz), and the left and right pre-auricular points (LPA and RPA)" [1].
• "in line with the 10-20 electrode placement standard, the terms Nasion and Left/Right Pre Auricular point (LPA/RPA) are used to refer to the anatomical landmarks used to determine the electrode placement."
• "In the documentation below we refer to anatomical landmarks such as the Left Pre Auricular point (LPA) and the Right Pre Auricular point (RPA), or the left and right Helix-Tragus Junction (LHJ, RHJ)." [3]
• "The head coordinate frame is defined through the coordinates of anatomical landmarks on the subject’s head: usually the Nasion (NAS), and the left and right preauricular points (LPA and RPA)." [4]

[1] R. Oostenveld and P. Praamstra. The five percent electrode system for high-resolution EEG and ERP measurements. Clin Neurophysiol, 112:713-719, 2001.
[2] Fieldtrip
[3] BIDS
[4] MNE