Polymake.jl 0.5.1 released

Today Polymake.jl 0.5.1 has been released.

Diff since v0.5.0

Merged pull requests:

• workflow: add ssh key secret for tagbot to allow triggering of documenter (#319) (@benlorenz)
• update badges (#320) (@benlorenz)
• bump libpolymake_julia to 0.2 (#324) (@benlorenz)