doc of text-properties-at needs to be clarified

[Drew Adams]

Doc string:

 Return the list of properties of the character at POSITION in
 OBJECT....

"list of properties" is misleading here. One might easily think that
the value would be a simple list of the text properties at that
position (e.g (face category display)), whereas it is a property list
of such text properties and their values.  That is, the list includes
both the text properties and their values.

Elisp manual:

 This function returns the entire property list of the character at
 POSITION in the string or buffer OBJECT.  If OBJECT is `nil', it
 defaults to the current buffer.

This is much better. However, this (like the doc string), never
mentions that the properties in the returned property list are text
properties. 

"Property list of the character" is not a good way to describe this,
because we don't usually think of characters as having property
lists. Symbols have property lists (and there are disembodied property
lists); characters have text properties, which have values.

This is a list that has the form of a property list, and it is
composed of the character's text properties with their values.