Add breaking changes and release 1.0.0.

lib/src/span_scanner.dart

Index: lib/src/span_scanner.dart
diff --git a/lib/src/span_scanner.dart b/lib/src/span_scanner.dart
index dd7f0e4f2e261b99b5265c161bdfa8e6e94081ff..043021b4d361b1c58a7ea1fa3b54d8e1cb774952 100644
--- a/lib/src/span_scanner.dart
+++ b/lib/src/span_scanner.dart
@@ -38,7 +38,10 @@ class SpanScanner extends StringScanner implements LineScanner {
   ///
   /// This is the span for the entire match. There's no way to get spans for
   /// subgroups since [Match] exposes no information about their positions.
-  FileSpan get lastSpan => _lastSpan;
+  FileSpan get lastSpan {
+    if (lastMatch == null) _lastSpan = null;
+    return _lastSpan;
+  }
   FileSpan _lastSpan;
 
   /// The current location of the scanner.
@@ -102,7 +105,7 @@ class SpanScanner extends StringScanner implements LineScanner {
     if (position == null) {
       position = match == null ? this.position : match.start;
     }
-    if (length == null) length = match == null ? 1 : match.end - match.start;
+    if (length == null) length = match == null ? 0 : match.end - match.start;
 
     var span = _sourceFile.span(position, position + length);
     throw new StringScannerException(message, span, string);