Add support for DSO and non-DSO WITec MatLab files

[GegznaV]

By @GregoryHuff in #8 (comment):

Not sure you all are aware that there are at least two different formats of WITec MatLab files. I put a brief explanation in the comments. More info is here and in WITec help.

The files in inst\extdata\mat.Witec all appear to be DSO type. It would be good to add some non-DSO ones to the unit test, I suppose.

@cbeleites Should this be included in the Milestone for hyperSpec 1.0 release?

Related:

• WITec matlab wavelengths #8

[GregoryHuff]

Here are three WITec files containing identical data.
_DSO is in the DSO format with cm-1 units.
The other two are in the non-DSO format. The _nm one has nm units instead of cm-1, which is kind of trivial.
KVan_matlab.zip