Update of the IME API spec

Hi all,

It's been a while since the last update for the IME API spec in April.
I would like to push this version to publish a new working draft.

Here's the current cut of editor's draft:
https://dvcs.w3.org/hg/ime-api/raw-file/default/Overview.html
(and log https://dvcs.w3.org/hg/ime-api/log)

Any comments are welcome.

Here are highlights of the changes since the last working draft (20130404):

* Example/use cases/best practices
- Removed Javascript IME use-case
- Removed example1 (drawing composition text in <canvas>)
- Added example code for drawing composition text.
- Added an explanation of InputMethodContext's scope in best practices
section.

* API
- Added target attribute proposed by Microsoft [1]
- Renamed getInputContext() to .inputMethodContext per comment from James Su
  [2]
- Marked composition and target attributes as nullable.
- Clarified that context is associated with one editable or focusable
element.
- Clarified the scope of setCaretRectangle()'s coordinates.
- Removed confusing 'enabled' property and open() method in favor of
  usual focus control and inputmode attribute.
- Changed composition interface. the 'text' property was changed to plain
  DOMString from Node, the 'caret' property was divided into the
  'selectionStart' and the 'selectionEnd' properties.  Added the 'segments'
  property to represent the position of segmentation of composition text.

[1] Microsoft proposal:
  https://dvcs.w3.org/hg/ime-api/raw-file/tip/proposals/IMEProposal.html
[2] Comment from James Su
  http://lists.w3.org/Archives/Public/public-webapps/2013AprJun/0361.html

Thanks in advance,
-- 
Takayoshi Kochi