handling fastText dependency

utils/similarity/__init__.py

@@ -0,0 +1,12 @@
+# from https://stackoverflow.com/questions/563022/whats-python-good-practice-for-importing-and-offering-optional-features
+import sys
+
+try:
+    import fastText
+except ImportError:
+    fastText = None
+
+if fastText is None:
+    print("In order to use slither-simil, you need to install fastText 0.2.0:")
+    print("$ pip3 install https://github.com/facebookresearch/fastText/archive/0.2.0.zip --user")
+    sys.exit(-1)