returns extension for a file path
extension = fileext(fullpath)
:fullpath a string matrix, the given file path : :extension a string matrix, the extension part is any or ‘’ :
`extension=fileext(`fullpath`_)` splits the fullpath character string in the extension part including the dot.
extension = fileext('SCI/etc/scilab.start')
extension = fileext(['SCI/etc/scilab.start';'SCI/etc/scilab.quit'])