simplify formatting of attributes
simplify formatting of attributes

Simplify the attr_map structure to be (attr_key, attr_value) ->
css_style.  Include the foreground and background colors in this
structure so they don't have to be special-cased.  This all makes the
code much shorter and easier to read.

MarkLodato/vt100-parser,MarkLodato/vt100-parser