Update all.bib
Update all.bib

Correcting accidental deletion. Note that there are multiple versions of the same entry, and unused items should probably be pruned.
stan-dev/stan,stan-dev/math,stan-dev/math,stan-dev/math,stan-dev/math,stan-dev/math,stan-dev/stan,stan-dev/stan,stan-dev/math,stan-dev/math,stan-dev/math,stan-dev/math,stan-dev/stan,stan-dev/stan