Fixed reading ReSentences with empty value

Changed RegEx to allow for sentences with empty values.
Fixes danikf#97

tik4net/Api/ApiSentence.cs

@@ -22,7 +22,7 @@ public string Tag
 
         public ApiSentence(IEnumerable<string> words)
         {
-            Regex keyValueRegex = new Regex("^=?(?<KEY>[^=]+)=(?<VALUE>.+)$", RegexOptions.Singleline);
+            Regex keyValueRegex = new Regex("^=?(?<KEY>[^=]+)=(?<VALUE>.*)$", RegexOptions.Singleline);
             foreach(string word in words)
             {
                 Match match = keyValueRegex.Match(word);