Add fluid methods to `PointerBuf`

[chanced]

Add fluid methods to Pointer that mutate in place and return a new instance.

• with token appended
• with token prepended
• with first token removed (maybe? - dont know whether to send the token into the void)
• with last token removed (same ^^)

this is somewhat obnoxious to deal with:

let mut instance_location = self.instance_location.clone();
instance_location.push_back(instance.into());
let mut keyword_location = self.keyword_location.clone();
keyword_location.push_back(keyword.into());