Allow using system-provided library

[gspr]

Automatic downloading and building of third party libraries without the user's consent is somewhat bad form. It would be nice if rivet would let the user manage such libraries themselves.

[mlesnick]

Hi, thank you for the input. I realize that the auto-installs of MessagePack and docopt are not mentioned in the documentation, and this should be addressed. Would this be sufficient?

[gspr]

mlesnick <notifications@github.com> writes:

Hi, thank you for the input. I realize that the auto-installs of MessagePack and docopt are not mentioned in the documentation, and this should be addressed. Would this be sufficient?

I'd still say that it would be very useful to have an option to override these things. It's not great that a *build system* reaches out to the internet and downloads and compiles third-party code.