TextWrangler for Mac does not have an HTML Entities palette built in to easily put special characters and symbols into your code. Is there a way to download one and integrate it into the program?
TextWrangler is a sunsetted product. Bare Bones software no longer updates it or supports it.
You might want to look into BBEdit, the grandfather of Mac code editors. BBEdit has a free mode where certain features are not available. I've been using it since the "Classic Mac OS" days so I am not sure what the pulled features are in the free version. But BBEdit does have exactly what you are looking for, it's a fabulous bit of Mac code. What other app can get away with the tag line "it doesn't suck?!"
(Note, I have no financial -or otherwise- interest in Bare Bones Software, just a happy customer.)