Use onig-config to get library/include dirs

[jrjsmrtn]

This fixes #72 in a more standard way than #73, by using onig-config.

[asottile]

I'd rather not add the complexity for nonstandard build situations

[jrjsmrtn]

I'd rather not add the complexity for nonstandard build situations

I don't understand ??? :-/

Using the MacPorts or Homebrew package managers is pretty standard on macOS. Using onig-config to get the onigurama config also seems pretty standard to me.

On the win32 platform, you configure dirs to get to the ONIGURAMA_CLONE installation.

Could you please reconsider ? I'm trying to get help and help building oniguramacffi on macOS here... and using CPATH is not a standard way of installing... :-/

[asottile]

it already works fine with homebrew

[jrjsmrtn]

it already works fine with homebrew

OK, good to know... I had no macOS with Homebrew to test, I just checked the onigurama recipe.

But my issue and PR are with MacPorts, which a lot of people are also using. :-/