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.
However this is not DRY, violates the "change one-line principal" and introduces potential for human error... hence this approach.

Also, there are about 28 formula that use this version syntax.  A possible alternative would be to add or adjust a token class in `version.rb`.  Of the specified versions (~308), fixing simple hyphenated version parsing would eliminate `version`s for at least this many (~50% of hyphenated versions).  That would cut total formula `version`s by ~10%.