handle backspace in all begining of line cases
handle backspace in all begining of line cases

Browserb differ in behavior -- currently non-problematic but still
different. Ex. In a code block Chrome will delete the <pre> tag whereas
Firefox does nothing.

willrowe/quill,voxmedia/quill,sferoze/quilljs,quilljs/quill,willrowe/quill,quilljs/quill,voxmedia/quill,quilljs/quill,sferoze/quilljs,sferoze/quilljs,voxmedia/quill,willrowe/quill,sferoze/quilljs