Add project files.

Beam.Exports/Exporter.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Beam.Exports {
+    public class PlainTextExporter : IExporter, IAsyncExporter {
+        public PlainTextExporter(IDocument document) {
+            Document = document;
+        }
+
+        public IDocument Document { get; }
+
+        protected virtual string Convert() {
+            return Document.ToString();
+        }
+
+        protected virtual Task<string> ConvertAsync() {
+            return Task.FromResult(Document.ToString());
+        }
+
+        public virtual void Write(string path) {
+            var text = Convert();
+            if (!Directory.Exists(Path.GetDirectoryName(path)))
+                throw new ArgumentException(S.M.FileDirectoryDoesNotExist, nameof(path));
+            File.WriteAllText(path, text, Encoding.Unicode);
+        }
+
+        public virtual async Task WriteAsync(string path) {
+            var text = await ConvertAsync();
+            if (!Directory.Exists(path))
+                throw new ArgumentException(S.M.FileDirectoryDoesNotExist, nameof(path));
+            await File.WriteAllTextAsync(path, text);
+        }
+    }
+}