Conflict with ibus IME if highlighting is enabled

I'm integrating codejar with my [personal website](https://quan.hoabinh.vn/), a Vietnamese blog. I use ibus-unikey, on Ubuntu, to input Vietnamese, and encounter an issue that, very often, uncommited chars are lost.

I found that codejar is relying on `event.isComposing` to detect if the IME is in its task. But actually, it is not reliable. You can read more here: https://lists.w3.org/Archives/Public/public-editing-tf/2015Nov/0001.html