Singular.jl 0.13.0 released

Today Singular.jl 0.13.0 has been released.

Diff since v0.12.0

Merged pull requests:

• more efficient saturation (#588) (@tthsqe12)
• fix keyword oops (#589) (@tthsqe12)
• remove bad ordering_M definition (#590) (@tthsqe12)