Singular.jl 0.5.3 released

Today Singular.jl 0.5.3 has been released.

Diff since v0.5.2

Closed issues:

• Scalar multiplication is missing for ideals (#43)
• method error on fractions (#350)
• coeff (correctly) not implemented for spoly used by various functions (#398)
• lead_exponent -> leading_exponent_vector (#403)
• Bug for rationals (#419)

Merged pull requests:

• scalar multiplication of ideals by polynomials (#415) (@tthsqe12)
• leading coefficient stuff (#417) (@tthsqe12)
• Add fancy orderings (#418) (@tthsqe12)
• more gc protection for coeffs, polys, and ideals (#420) (@tthsqe12)
• fix reference bugs (#421) (@tthsqe12)
• Bump Nemo and AA version (#423) (@thofma)
• fix leaks (#425) (@tthsqe12)
• start basic error checking (#426) (@tthsqe12)
• fix nullptr TODO (#427) (@tthsqe12)
• n_algExt -> n_transExt conversion (#428) (@tthsqe12)
• Unbreak master (#430) (@thofma)
• bump version to 0.5.3 (#432) (@tthsqe12)