Added build file for osx/nix.

Author: merbla

build.sh

@@ -0,0 +1,13 @@
+#!/bin/bash
+dotnet --info
+dotnet restore
+
+for path in src/**/*.csproj; do
+    dotnet build -f netstandard1.3 -c Release ${path}
+    dotnet build -f netstandard2.0 -c Release ${path}
+    
+done
+
+for path in test/*.Tests/*.csproj; do
+    dotnet test -f netcoreapp2.0 -c Release ${path}
+done