v1.0.0

• Potentially breaking change (hence version 1.0.0): rename ESGtoolkit to esgtoolkit (announced here). Also, more consistent with the package naming in R universe

• include ycinter and ycextra, respectively for yield curve interpolation and extrapolation (comes from package ycinterextra, which will be discontinued (my choice) and has already been unilaterally removed by the CRAN landlords)