hu-old-hungarian-rovas: several improvements, most of them suggested …

…by Viktor Kovács <kov.h.vik@gmail.com>

- Add missing small "ent", "emp", "unk", "us" and "amb" symbols to hu-old-hungarian-rovas.txt

  Resolves: #33

  Also add typing variants for the capital symbols typing only the first
  or the first two Latin letters in upper case.

- Add missing small and capital "enc", "and", "ech", "ent shaped sign" to hu-old-rovas.txt

  Resolves: #34

  Typing sequences for “ent shaped sign” are “ents” (small), “Ents”, “ENTs”, “ENTS” (capital).

- Follow Sándor Forrai’s orthography for ü, Ü, ű, Ű

  Resolves: #30

- add small and capital "short R"

  Resolves: #31

- Add U+200D ZERO WIDTH JOINER, U+200F RIGHT-TO-LEFT MARK, U+200C LEFT-TO-RIGHT MARK

  Resolves: #35

- Add Old Hungarian Numbers

  Resolves: #32

- Add reversed question mark, reversed comma, reversed semicolon

- Use `/` as a prefix for characters which are typed with AltGr on the xkeyboard-config old hungarian layout
  (We cannot use AltGr in ibus-table, so we can only use some prefix character instead)

- Use `/` as a prefix for ligature names

  Resolves: #29

  These ligatures are apparently very rarely used, making them accessible only with this prefix
  keeps them available if one really wants them but removes the possibility of them conflicting with
  something else.

- Use `_` as a prefix for characters accessed by a longer string like a shorthand of their name

- Add / and _ to also input themselves

  / is uses as a prefix similar to AltGr and _ as a prefix to input characters by name but one should
  still be able to input / and _ themselves.

- Add Latin postfix input

  To make it usable with almost any keyboard layout, not only with the Hungarian keyboard layout.