add unsafe versions for datafilter class in c# (#618)

Signed-off-by: Andrey Parfenov <a1994ndrey@gmail.com>

Author: Andrey1994

csharp_package/brainflow/brainflow/brainflow.csproj

@@ -4,4 +4,12 @@
     <TargetFramework>netstandard2.0</TargetFramework>
   </PropertyGroup>
 
+  <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Debug|AnyCPU'">
+    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
+  </PropertyGroup>
+
+  <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Release|AnyCPU'">
+    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
+  </PropertyGroup>
+
 </Project>