- Remove os.glob, which was easy to misuse
- Accept string literals anywhere string lists are expected, including
  the include and exclude parameters of glob
- Replace regexp-based globbing with github.com/pgavlin/glob, which
  offers an expanded syntax and improves performance by making fewer
  system calls

This is a breaking change: patterns like '**.go' will no longer match
all files ending in ".go" in a directory tree. These patterns must be
replaced with '**/*.go'.