Preparing dealer.c for make

Before turning our focus to make, we need to first revisit the header file organization we used in our dealer program. In that set of files, we took a simplistic approach where every source file included the same header file, dealer.h, which itself included all the header files from each of the source files. This was a shortcut that is not typical of most C source files. Including all the header files in a single header file and then only including that one file has limiting and possibly undesirable implications. First, doing this assumes that all source files are bound together and interdependent. Second, it means if any source file or header file changes, we must recompile all of the files to regenerate the program. For projects with many files, this means a lot of unnecessary work needs to be done; instead, we’d like to just compile the files that change and then link the unchanged and changed files together. We cannot do that with our previous...