FULL_WIDTH_TODO

* 2-bytes characters ARE NOT necessary full-width char, and 1-byte characters ARE NOT necessary half-width char.
* So ScreenBuffer Char Size should be kept to 4 bytes.
* Some flags should be used to detect full-width char: LEADING_FULLWIDTH and TRAILING_FULLWIDTH.
* A full-width char is written down on two cell, it should have exactly the same data (style, color, etc) except the 
	LEADING_FULLWIDTH for the first and the TRAILING_FULLWIDTH for the last
* Replace Buffer#writeUInt32BE() by Buffer#writeInt32BE() because 128 << 24 = -2147483648 (signed)