add poly parameter in diso() function

a precursor-dereived metabolite might be the modification of the dimer , trimer or even polymer of the precursor. For instance, [2Try   x   H] . In this situation, the mass difference of this labeled and unlabed metabolite will be 2 times of this labeled precursor. Poly parameter is therefore used to catch this kind of metabolotes.

Merge branch 'master' of https://github.com/YonghuiDong/Miso

Merge branch 'master' of https://github.com/YonghuiDong/Miso

Update Rresult() function to remove natural isotopes

Update README.md

Merge remote-tracking branch 'origin/master'