fix ie position error. ichord/At.js#123

while using `textRange.movetoBookMark` and `range.getBookMark()`
and the caret is at the ending, the textRange's boundings was wrong.

maybe there is no bookMark at the end of line in IE8
stupid mistake of getting offset in ie

there is no return value to offset in IE < 8 browser
update version to v0.0.5