v1.4.2

• Implement gradients for the covariance kernels through the k_grad method
• Implement mellon.cov.Linear covariance kernel
• Change logging setup to configuration dict
• allow setting active_dims for composit kernels, allowing more flexible covariance kernel specifications
• update jaxconfig impot for compatibility with jax>=0.4.25 (s. deprecation of jax.config.config)
• generalize variing sigma in FunctionEstimator for higher dimensional functions