added new syntax highlighting files

I added a sample etc/hosts file and a sample requirements.txt file. I didn't know there was already a sample YAML file because it wasn't ticked in the issue so I added some extra syntax that I had in my own to the previous  example.yaml file.

tests/syntax-tests/highlighted/RequirementsTXT/requirements.txt

@@ -0,0 +1,8 @@
+#this is a sample requirements.txt file
+
+django==11.2.0
+pywheels>=12.4 #a whitespace followed by comments
+Nuitka<0.6.8.4
+wxPython>=1.0, <=2.1
+
+#this is another comment