vkb format for OS2007/OS2008/Maemo5

- released into public domain (Permission is granted, free of charge, to any
  person obtaining a copy of this file, to deal with the file without
  restriction, including without limitation the right to use, copy, modify,
  merge, publish, distribute, sublicense, and/or sell copies of it. The file
  is provided "as is", without warranty of any kind.)
- this is the third version of the document
- changelog:
  - v1: initial version based on reverse engineering of vkb files
  - v2: revised using the excellent work by Kimmo Jukarainen,
    http://idoru.metadreams.net/~kimju/src/maemo/decode_vkb/
  - v3: added 0x80 key flag
  - v4: added info about raw keys and missing key flags

- multibyte fields are little endian
- everything is utf-8 encoded
- all numbers in the "description" column are written in hexadecimal
- some (all?) length fields can be zero
- strings are denoted as 1+n and are encoded as:
	bytes	description
	1	length of the next field, in bytes
	n	the string (utf-8 encoded)

GLOBAL HEADER
bytes	description
1	version (01)
1	number of sections (02 for normal and thumb kbd, 01 for special kbd)
1+n	descriptive (human-visible) name of the locale
1+n	locale name (e.g. en_GB)
1+n	locale name of a word completion dictionary
1	number of screen modes supported by this keyboard (02)
n	types of individual screen modes (1 byte each; types are:
	0 = normal, 1 = thumb, 2 = rotated) (00 01)
1	number of key sizes (05)
...	KEY SIZE
...	KEY SIZE
	(default key sizes are:
	23 23 1a 00 00  32 23 1a 00 00  37 23 1a 00 00  48 37 29 00 00  8f 37 29 00 00
	that's: 00 normal key, 01 longer key used on the right side of odd
	rows, 02 more longer key used on the left side of odd rows, 03 big
	key used in thumb kbd, 04 double width big key used in thumb kbd)
	(for special kbd, default key sizes are: 23 23 1a 00 00)
2	absolute offset in the file of the first section
2	absolute offset in the file of the second section
	...
20	zeros
...	SECTION
...	SECTION

KEY SIZE
bytes	description
1	width of a key (in pixels? rather seems to be percentage or something)
1	height of a key
1	offset of a text (from the top of the key to the bottom of the text)
	- i.e. baseline
1	left padding (extra value, not included in the width)
1	top padding (extra value, not included in the height)

SECTION HEADER
bytes	description
1	type of the section (00 normal kbd, 01 special kbd, 04 thumb kbd;
	other values: 03 large kbd, 05-07 east language kbds, 08 stroke kbd)
1	number of layouts (02 for normal kbd, 04 for thumb kbd, 06 for special kbd)
1	numeric kbd (00); the meaning of this field is unclear
1	default key size (00 for normal kbd, 03 for thumb kbd, 00 for special kbd)
...	LAYOUT
...	LAYOUT

LAYOUT HEADER
bytes	description
1	layout type (00 lowercase, 01 uppercase, 02 neither - i.e. special chars)
	notes:
	- in a special kbd, even tabs with letters are of the 02 type
	- it seems to be hard-coded that the first two layouts in a special
	  kbd have the shift key disabled
1	corresponding other case layout number, counted from 0; ff for
	a single case layout
1+n	name of the layout (in normal kbd should be empty; in thumb kbd
	should be 3 utf-8 chars; in special kbd corresponding lower/upper
	layouts should have the same name)
1	number of sublayouts (normal kbd has 2 sublayouts, thumb kbd and
	special kbd have 1 sublayout)
...	SUBLAYOUT
...	SUBLAYOUT

SUBLAYOUT HEADER
bytes	description
1	number of keys in the sublayout
1	number of rows of the sublayout
1	left margin (in pixels?) (9 for numeric kbd)
1	top margin
1	bottom margin
1	right margin (seems that setting of margins affects also other
	sublayout margins in some strange way)
n	number of keys in individual rows (1 byte for each row)
...	KEY
...	KEY

KEY
bytes	description
1	key type (00 normal key, 01 sliding key, 02 modifier key, 04 multiple key)
...	these fields depend on the key type (KEY_NORMAL, KEY_SLIDING, etc.)

KEY_NORMAL
bytes	description
1 or 2	FIELD_KEY_FLAGS
1+n	letter
1	key size
if raw key flag is set
1+n scancode data

KEY_SLIDING
bytes	description
1 or 2	FIELD_KEY_FLAGS
1	number of keys on the sliding key | 0x80
1+n	letter
1+n	letter
	...
1	key size
if raw key flag is set
1+n scancode data

KEY_MODIFIER
1 or 2	FIELD_KEY_FLAGS
1+n	letter
1	key size
if raw key flag is set
1+n scancode data

KEY_MULTIPLE
bytes	description
1	number of keys
...	KEY
...	KEY

FIELD_KEY_FLAGS
bytes	description
1	key flags (bitfield)
	bits:	0 (0x01)	alpha
		1 (0x02)	numeric
		2 (0x04)	hexa
		3 (0x08)	telephone
		4 (0x10)	special
		5 (0x20)	dead
		6 (0x40)	whitespace
		7 (0x80)	next byte is continuation of the flags
1	present only if the previous field contains 0x80 flag:
	more key flags (bitfield?)
	bits:	0 (0x01)	raw key
		1 (0x02)	tone
		2 (0x04)	draw tab face over the key
		3 (0x08)	draw backspace face over the key
		4 (0x10)	draw shift face over the key