Fixed the checking of xs
Updated the position vector functions to handle [1x3] or [1x6] vectors
Added the new conf.driving_functions flag to the config file
Fixed a bug in isargposition, now it works with [1x3] and [1x6]
Fixed a bug in position_vector(), now it returns again something
Updated the secondary_source_selection to use xs for the direction of focused s.
Changes secondary_source_selection() to the new syntax in all files
Fixed vector_norm for nk calculation
Updated comments
Added the new focused source xs syntax to test_driving_functions()
Added helper file to check for xs ([1x3] or [1x6])
Replaced position_vector() with isargposition() and isargxs()
Fixed secondary_source_selection() to work with a pure direction vector for fs
Made the new fs direction handling work with the WFS driving functions
Updated the NEWS file
Include 2D, 2.5D, 3D and conf.driving_functions into the imp WFS driving functions