Correct dataTypeIndex ambiguous definition

[HanBnrd]

Fixes #87

Corrects the dataTypeIndex ambiguous definition to clarify that it is indeed an integer (and not a numeric 1-D array).

Elements that have also been checked for coherence with this PR:

• dataType
• dataTypeLabel
• detectorModuleIndex
• probe/wavelengths
• probe/frequencies
• probe/timeDelays
• probe/timeDelayWidths
• probe/momentOrders
• probe/correlationTimeDelays
• probe/correlationTimeDelayWidths
• Appendix

[samuelpowell]

Rather than say

Note that the Time Domain and Diffuse Correlation Spectroscopy data types have two additional parameters and so the data type index is used to map both those additional parameters with the same index.

Why not

Note that where multiple parameters are required the same index must be used into each (examples include data types such as Time Domain and Diffuse Correlation Spectroscopy).

The latter is more general and reduces coupling.

[dboas]

@samuelpowell this has two approvals. Do you want to merge it?