add plain tokenizer tests for uncovered lines and add editorconfig

src/.editorconfig

@@ -0,0 +1,2 @@
+root = true
+[*.cs]

src/UglyToad.PdfPig.Tests/Tokenization/PlainTokenizerTests.cs

@@ -0,0 +1,35 @@
+namespace UglyToad.PdfPig.Tests.Tokenization
+{
+    using PdfPig.Tokenization;
+    using PdfPig.Tokenization.Tokens;
+    using Xunit;
+
+    public class PlainTokenizerTests
+    {
+        private readonly PlainTokenizer tokenizer = new PlainTokenizer();
+
+        [Fact]
+        public void TextNullReturnsNullToken()
+        {
+            var input = StringBytesTestConverter.Convert("null ");
+
+            var result = tokenizer.TryTokenize(input.First, input.Bytes, out var token);
+
+            Assert.True(result);
+
+            Assert.Equal(NullToken.Instance, token);
+        }
+
+        [Fact]
+        public void TryTokenizeWhitespaceFalse()
+        {
+            var input = StringBytesTestConverter.Convert("    something");
+
+            var result = tokenizer.TryTokenize(input.First, input.Bytes, out var token);
+
+            Assert.False(result);
+
+            Assert.Null(token);
+        }
+    }
+}

src/UglyToad.PdfPig.sln

@@ -7,6 +7,11 @@ Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "UglyToad.PdfPig", "UglyToad
 EndProject
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "UglyToad.PdfPig.Tests", "UglyToad.PdfPig.Tests\UglyToad.PdfPig.Tests.csproj", "{5BA09F66-5706-4637-B083-E1DC4D53289B}"
 EndProject
+Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "Solution Items", "Solution Items", "{C55738D2-3165-4D03-9CE2-10A2E2EEC465}"
+	ProjectSection(SolutionItems) = preProject
+		.editorconfig = .editorconfig
+	EndProjectSection
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU