Error for some special characters when running `doi2pdf` about mathbin

[gerw]

It seems that your grep is missing -P for perl regexp.

[kellertuer]

Hm, that is interesting, because it is the same machine I wrote the tutorial for that is now in the Readme and I am not aware of having changed grep.

Edit: Maybe it would be better to have these script really a little bit more system independent. The only thing keeping me from starting that is, that the php code is really not that easy to read, i.e. a little hard to understand what it does and how it is actually done. Maybe I‘ll try to reimplement this in one language without so many dependencies at some point.