Describe build options in README (e.g. cairo-features.h)

[tannerhelland]

I am currently custom-building cairo for some homebrew VB6 projects (using an msys2-based build chain modeled after https://github.com/preshing/cairo-windows/), but would prefer to switch to this community-supported project. Certain additions to the README would be helpful as the current one raises many questions!

For example, what cairo features are included in this build? Cairo exposes a ton of compile-time features, and there is worthwhile discussion over what is even useful in a windows build. (For example, is it worthwhile to add libpng to the build when GDI+ already provides PNG support? What about FreeType, which has certain advantages/disadvantages vs GDI?)

Short of manually spelunking into the lib/rcairo-xxx/build folder and inspecting this repo's win32 makefiles, it's not clear what this build includes. Stating build options up-front on the README would be very helpful.

[wqweto]

This project needs much love as is. For instance I actually have no idea how to build the binary in bin (don't see src/build.bat or similar automation).

Sent you an invite for the org if you are intrested to join the effort. Probably @thetrik can chime in how to continue.

[tannerhelland]

Thanks @wqweto. TBH a bare dll with no build script is exactly what Olaf gets criticized for, as it's non-compliant with the LGPL (e.g. see section 3.4, "avoid the Build Guru").

Even if that is rectified, given the perf state of this build (#7) users should probably be advised to use Olaf's build anyway which seems counterproductive to this "more open" effort!

I'm happy to help but don't want to step on @thetrik toes, so will wait for further instruction from him before posting any PRs or similar.