vs2017: add cmake-settings

Visual Studio 2017 can open CMake projects directly, but having a
CMakeSettings.json file in the repo will make the IDE know about the
build configurations we support.

CMakeSettings.json

@@ -0,0 +1,56 @@
+{
+  "configurations": [
+    {
+      "name": "Debug",
+      "generator": "Ninja",
+      "configurationType": "Debug",
+      "inheritEnvironments": [
+        "msvc_x86"
+      ],
+      "buildRoot": "${env.USERPROFILE}\\CMakeBuilds\\${workspaceHash}\\build\\${name}",
+      "installRoot": "${env.USERPROFILE}\\CMakeBuilds\\${workspaceHash}\\install\\${name}",
+      "cmakeCommandArgs": "",
+      "buildCommandArgs": "-v",
+      "ctestCommandArgs": ""
+    },
+    {
+      "name": "Release",
+      "generator": "Ninja",
+      "configurationType": "Release",
+      "inheritEnvironments": [
+        "msvc_x86"
+      ],
+      "buildRoot": "${env.USERPROFILE}\\CMakeBuilds\\${workspaceHash}\\build\\${name}",
+      "installRoot": "${env.USERPROFILE}\\CMakeBuilds\\${workspaceHash}\\install\\${name}",
+      "cmakeCommandArgs": "",
+      "buildCommandArgs": "-v",
+      "ctestCommandArgs": ""
+    },
+    {
+      "name": "RelWithDebInfo",
+      "generator": "Ninja",
+      "configurationType": "RelWithDebInfo",
+      "inheritEnvironments": [
+        "msvc_x86"
+      ],
+      "buildRoot": "${env.USERPROFILE}\\CMakeBuilds\\${workspaceHash}\\build\\${name}",
+      "installRoot": "${env.USERPROFILE}\\CMakeBuilds\\${workspaceHash}\\install\\${name}",
+      "cmakeCommandArgs": "",
+      "buildCommandArgs": "-v",
+      "ctestCommandArgs": ""
+    },
+    {
+      "name": "MinSizeRel",
+      "generator": "Ninja",
+      "configurationType": "MinSizeRel",
+      "inheritEnvironments": [
+        "msvc_x86"
+      ],
+      "buildRoot": "${env.USERPROFILE}\\CMakeBuilds\\${workspaceHash}\\build\\${name}",
+      "installRoot": "${env.USERPROFILE}\\CMakeBuilds\\${workspaceHash}\\install\\${name}",
+      "cmakeCommandArgs": "",
+      "buildCommandArgs": "-v",
+      "ctestCommandArgs": ""
+    }
+  ]
+}