pkgbuild 1.4.1

• New Config/build/extra-sources DESCRIPTION option to make pkgbuild aware
  of extra source files to consider in needs_compile().

• New Config/build/bootstrap DESCRIPTION option. Set it to TRUE to run
  Rscript bootstrap.R in the package root prior to building the source
  package (#157, @paleolimbot).

• pkgbuild now supports Rtools43.

• pkgbuild now always appends its extra compiler flags to the ones that
  already exist in the system and/or user Makevars files (#156).