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.
Homebrew doesn't have a "change one-line principle". It can never have a "change one-line principle" because with pretty much every new formula and update processed both the version and the checksum have to be updated, as well as patches checked and removed or rebased as necessary. Sadly, it is hard to run a package manager in a way that *doesn't* introduce the possibility for human error in places.

Homebrew rarely uses ``` version ``` in the way you are thinking it does on this. Homebrew tends to use ``` version ``` to monitor releases and make things tidier for end users in situations where the url is something like ``` foo20142192bz1p ```. It isn't usually intended as a drop-in replacement for the ``` "https://github.com/steakknife/makeheaders/archive/#{version}.tar.gz" ``` situation.