support iframe

releated issues #124
Merge branch 'iframe'
update version to 0.4.5
fix issues #128

wrong document error
fix get range error in textarea
Merge branch 'fix-ie-bug'
index.html: better behave for iframe in ie
Merge branch 'improve index.html'
update version to v0.4.6
fix issues #132

lose `range` while press `ENTER`.
maybe ckeditor had hack the enter event.
just `mark the range` before enter.
Merge pull request #1 from ichord/master

update