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/source/YAML/example.yaml

@@ -4,6 +4,9 @@ id: 3595
 name: Test User
 username: "testuser"
 other_names: ['Bob', 'Bill', 'George']
+hexa: 0x11c3 #inline comment
+octa: 021131
+lastseen: .NAN
 enabled: true
 locked: false
 groups: 
@@ -13,6 +16,19 @@ groups:
 address: >
   123 Alphabet Way
   San Francisco, CA
+bio: |
+  I am a hardworking person
+  and a member of the
+  executive staff
 phone: null
+email: ~
 building_access: yes
-secure_access: no
+secure_access: no
+bulb: On
+fans: Off
+emails:
+    executives:
+      - bob@example.com
+      - bill@example.com
+    supervisors:
+      - george@example.com