3rd official release: allow a better tuning of the RAW reader

This version allows to specify which RAW reader should be used with e.g.:

addpath /path/to/readraw
compile(readraw);               % checks for available readers and selects best
compile(readraw, 'compile');    % force manual compilation of e.g. unpackRaw and DCRAW
compile(readraw, 'dcraw_emu');  % use 'dcraw_emu' as reader

where you can give as 2nd argument dcraw_emu, dcraw, simple_dcraw, unpackRaw, libraw for use.