Bootstrap Slope Heterogeneity Test for Panel Data // Implements the bootstrap slope heterogeneity test for panel data based on Blomquist and Westerlund (2015) doi:10.1007/s00181-015-0978-z. Tests the null hypothesis that slope coefficients are homogeneous across cross-sectional units. Provides both standard and adjusted Delta statistics with bootstrap p-values. Supports partialling out of control variables and cross- sectional averages for dealing with cross-sectional dependence.