Cursor and marks positions are restored after the beautification
Zeus's code is used (with small changes) from here:
https://github.com/ZeusTheTrueGod/vim-format-js
Thank you Zeus.

Known bug: the 'last change mark' (.) restore doesn't work.
update README
add test for restore position patch
Fix multiple tabs are used for indentation (fix #11)
add test on multiple tabs for indentation (fix #11)