Add docs for String.bigrams() and String.similarity(text)

doc/base/classes.xml

@@ -37268,6 +37268,13 @@ This method controls whether the position between two cached points is interpola
 			Return true if the strings begins with the given string.
 			</description>
 		</method>
+		<method name="bigrams">
+			<return type="StringArray">
+			</return>
+			<description>
+			Return the bigrams (pairs of consecutive letters) of this string.
+			</description>
+		</method>
 		<method name="c_escape">
 			<return type="String">
 			</return>
@@ -37627,6 +37634,15 @@ This method controls whether the position between two cached points is interpola
 			<description>
 			</description>
 		</method>
+		<method name="similarity">
+			<return type="float">
+			</return>
+			<argument index="0" name="text" type="String">
+			</argument>
+			<description>
+			Return the similarity index of the text compared to this string. 1 means totally similar and 0 means totally dissimilar.
+			</description>
+		</method>
 		<method name="split">
 			<return type="StringArray">
 			</return>