Adds a BERT feature extractor (#116)

* Initial commit of BERTFeatureExtractor.

* Updates for the integrated version of WordpieceTokenizer.

* Repackaging org.tribuo.interop.onnx.bert to org.tribuo.interop.onnx.extractors.

* BERTFeatureExtractor now implements TextPipeline, so you can use it in a RowProcessor via TextFieldProcessor.

* Adding hugginface transformers to THIRD_PARTY_LICENSES.txt

* Adding copyright statements.

* Adding another constructor to BERTFeatureExtractor.

* Adding a test for example extraction.

* Relaxing the fp comparison.

* Fixing review comments.

Interop/ONNX/pom.xml

@@ -52,6 +52,16 @@
             <artifactId>tribuo-regression-core</artifactId>
             <version>${project.version}</version>
         </dependency>
+        <dependency>
+            <groupId>${project.groupId}</groupId>
+            <artifactId>tribuo-json</artifactId>
+            <version>${project.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>${project.groupId}</groupId>
+            <artifactId>tribuo-util-tokenization</artifactId>
+            <version>${project.version}</version>
+        </dependency>
         <dependency>
             <groupId>com.microsoft.onnxruntime</groupId>
             <artifactId>onnxruntime</artifactId>