0.3.0.0

• Implement sparse polynomials.
• Add GcdDomain and Euclidean instances.
• Add functions leading, monomial, scale.
• Remove function constant.

0.2.0.0

• Fix a bug in Num.(-).
• Add functions constant, eval, deriv, integral.
• Add a handy pattern synonym X.

0.1.0.0

• Initial release.