New features

[lbelzile]

• add blended GEV model
• inhomogeneous Poisson process with orthogonal parametrization
• New estimators of the tail dependence coefficient
• Add seismic activity data and Palm drought severity index
• add extremogram estimator with block bootstrap
• regression models for GEV, etc. by collapsing inequality constraints (all domain must be positive, so keep minimum)?
• estimator of extremal dependence