Possible improvements for TAXAassign

Hi Umer,

here are some coding style or simplifications I suggest for the TAXAassign shell script. Several of the conditional loops you use could be replace with one-liners ( [[test]] || die). Some tests regarding the status of files (exists, is empty, etc), could also be simplified by using the new pattern substitutions in bash 4.0. But unfortunately, many computer still have bash 3.0 installed.

Best,