IME support for East Asia users

[SadPencil]

An Input Method Editor (IME) is a software component that enables a user to input text in a language that can't be represented easily on a standard QWERTY keyboard. This is typically due to the number of characters in the user's written language, such as the various East Asian languages.

@frg2089 brought a PR for XNAUI to provide IME support in DX and XNA display engine, Rampastring/Rampastring.XNAUI#32 . Note that many Chinese mods that use forks of this client have already shipped with IME support for years, to meet the huge need of numerous players. Thus I think we should officially provide IME support before releasing a stable release -- if not, these users might have to seek for an unstable release just in order to type words.