Update YAML definition

This commit updates the Octo-YAML.tmLanguage definition to add support
for string literals, :stringmode, and :assert, based upon John's changes
to the XML in #2.

Octo.YAML-tmLanguage

@@ -44,12 +44,16 @@ patterns:
 
 - comment: Metaprogramming commands
   name: support.function.octo
-  match: (?<=^|\s)(?:\:macro|\:calc|\:byte)(?=$|\s)
+  match: (?<=^|\s)(?:\:macro|\:calc|\:byte|\:stringmode)(?=$|\s)
 
 - comment: Breakpoint command
   name: support.function.octo
   match: (?<=^|\s)(?:\:breakpoint)(?=$|\s)
 
+- comment: Assertion command
+  name: support.function.octo
+  match: (?<=^|\s)(?:\:assert)(?=$|\s)
+
 - comment: Memory monitor command
   name: support.function.octo
   match: (?<=^|\s)(?:\:monitor)(?=$|\s)
@@ -86,4 +90,10 @@ patterns:
   name: entity.name.function.octo
   match: (?<=^|\s):\s+\S+(?=$|\s)
 
-...
+- comment: String Literals
+  name: string.quoted.double.octo
+  begin: '"'
+  end: '"'
+  patterns:
+  - match: \\[tnrv0\\"]
+    name: constant.character.escape.octo