v3.1.2

Polynomials v3.1.2

Diff since v3.1.1

Closed issues:

• Negation of polynomial type unstable (#395)
• Should SparsePolynomial support negative exponents? (#409)

Merged pull requests:

• fix == of different types (#410) (@jverzani)
• Negative exponents in SparsePolynomial (#411) (@jishnub)
• fix invalidations (#412) (@jverzani)
• Jishnub sparseneg int der (#413) (@jverzani)
• fix doctest (#414) (@jverzani)