Improve Conanfile for consumers of the package

[JacobCrabill]

• Type 'make' to build and test the package in one go
• Fix issues with Conanfile - create a package which can be consumed by downstream Conan packages

The export_sources field of the conanfile was incorrect, preventing downstream packages from consuming this package.

I also took the liberty of making some changes to the Conanfile to make the build more "standard" and easier to work with (allowing the use of a simple Makefile to easily build & test the package).

[JacobCrabill]

@pboettch anything I can do to speed this along?

[pboettch]

Hmm, I have to admit that adding a GNU Makefile is not something I'd consider. Is this a common way for Conan-enabled projects?

[pboettch]

Especially that you Makefile does not really have dependencies, so a simple shell-script would do it the same way.

[JacobCrabill]

@pboettch a BASH script could do the same, but in my day job we've standardized on Makefiles as a somewhat simpler and intuitive method of implementing build scripts. This way, when you clone a repo following this convention, all you have to do is type make and you're done. With a BASH script, you first have to find the script, figure out if it needs any arguments, or search for the custom commands it exports, etc.

[JacobCrabill]

I can remove the Makefile from the PR if you'd like; the Conanfile changes are what's important. The Makefile is just a quality-of-life improvement with no downsides.

[pboettch]

Yes, please remove the Makefile and add instruction (and links) to the README-file for conan-users (if necessary).

[pboettch]

PR Merged (with rebase) manually.