rmk122--Next round on fonts and MCCS (#2280)

* A revision to the font, Unicode, Tedit, and other modules to implement the MCCS character coding as the standard for internal text strings.  MCCS is a variant of XCCS with arrows switched with circumflex/underscore and $ switched with currency, and allows for additional code assignments over time. :MCCS replaces :XCCS as the default external format, especially for source files.  The file XCCS is removed in favor of the file MCCS, which includes the XCCS external format for backward compatibility.

* This includes a single Medley-font formatted font file for each of the family/size/face display fonts.  The glyph assignments correspond to the MCCS character encoding (except for fonts with idiosyncratic encodings--Hippo, Symbol).  All charsets from legacy font files are included in each file, and the character sets and glyphs in each file have also been extended by offline coercion from related families (e.g. Glyphs not in legacy Terminal are taken from legacy Modern). There should be fewer black boxes, and character-display shouldn't change when you switch fonts.

* The Unicode mapping tables have been redefined to set up correspondences between Unicode and MCCS, not XCCS.  Separate XCCS to/from MCCS mapping functions are provided in the file MCCS; they are no longer included in INTERPRESS.

* TEDIT converts characters in legacy fonts to their new MCCS codes as it reads formatted files, marks the file as MCCS compatible and preserves the new codes on writing.

* Default keyboard assignments produce the MCCS uparrow and leftarrow for shift-6 and shift-hyphen, use Function-6 for circumflex and Function-10 for underscore.

See documentation in FONTCODECHANGES.TEDIT MCCS.TEDIT MEDLEYFONTFORMAT.TEDIT in docs/internal, and library/UNICODE.TEDIT.

Author: rmkaplan