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This pull request adds support for text arrows. Common code for the three drawing functions is now in one method.
Furthermore, a conversion for different positioning units is included in the merged text drawing. This allows to deal with second test figure from #394.

I think the conversion might cause some problems when the figure size in tikz differs from the figure size in Matlab. So in the future, a conversion to normalized or data coordinates might be better. 
there is even more work to do: the otherwise part leads only to a correct location for the text when the tikz figure has the size of the matlab figure. If the figure size is changed, this goes wrong. 

I think a good way would be, to extend convertUnits to support 'normalized' and 'data'. As you mentioned before, this would require to add a handle as further parameter.

This problem has already been in the code, before you merged this PR. The new changes just make it more obvious. So (I hope) the PR did not break anything.