Additive Mixed Meta-Analysis with Spline Meta-Regression // Fit additive mixed meta-analysis (AMMA) models, extending the 'mixmeta' package https://cran.r-project.org/package=mixmeta to allow for spline-based meta-regression. Functions combine features of 'mgcv' https://cran.r-project.org/package=mgcv for building spline components and 'mixmeta' for estimating general mixed-effects meta-analysis models.