New formula: makeheaders

A tiny but powerful utility from the sqlite and fossil folks (it's used by both projects) for more scalable C/C++ codebases (read: cheaper to maintain), in the flavor of source-also-declares-interface--style development, vaguely similar to Go (Golang).  `makeheaders` is the **source** preprocessor that generates headers that makes the magic happen.  Also, it can generate the externally-exported library header too (`-H` instead of `-h`)! 

The github packaging makes it available to everyone that likes versioning / automation, i.e., a package manager and/or configuration management.
The executable is runnable and exits with return status 0.

This is a simple, UNIX-philosophy, C header generation utility that does one thing really well.

Command-line is [here](http://www.hwaci.com/sw/mkhdr/makeheaders.html#H0005).