Update for VS2019

[cogwheel]

This supersedes #91 which is currently in a bugged state (leaving that open for Github to investigate)

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This change is 

[cogwheel]

@davidc604 I've been working with someone from Appveyor and the failure is due to a missing component on their end. I've successfully tested a build by remoting into the build machine, installing the missing component, and continuing the build. So once appveyor/ci#3058 is addressed it'll work.

[davidc604]

Reviewed 2 of 3 files at r1, 1 of 1 files at r2.
Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @cogwheel)

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README.md, line 57 at r2 (raw file):

* [CMake](https://cmake.org/download/)
* [OBS dependencies](https://obsproject.com/downloads/dependencies2017.zip) - **TODO** This is only used for libcurl. We should use something else
* [Pre-built WebRTC](https://github.com/caffeinetv/webrtc/releases/latest)

just curious, going forward are we going be providing our own flavor of .gn files or scripts for setting up and building the necessary pieces of webrtc that is needed for libcaffeine?

(if we're already doing that then just ignore me...

[cogwheel]

Reviewable status: complete! all files reviewed, all discussions resolved

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README.md, line 57 at r2 (raw file):

Previously, davidc604 (David C) wrote…

just curious, going forward are we going be providing our own flavor of .gn files or scripts for setting up and building the necessary pieces of webrtc that is needed for libcaffeine?

(if we're already doing that then just ignore me...

My hope was to keep the WebRTC build as vanilla as possible, so for now I'm just building the webrtc target like normal. I think there are some things it's building that don't need to be linked in though, so I may revisit that at some point to reduce the binary size.