add visible as an option for ace-jump-mode-scope
Use the overlay 'window property to replace the indirect buffer

Originally, I use the indirect buffer to resolve the case when the
same buffer is showing in different window. This solution comes to
some issue when try to recover the indirect buffer. After some
investigation, I found overlay support the 'window property which
limit that overlay to show on a specific window. This is definitely
a better solution for this case. So this change is comming.
Merge pull request #52 from aecay/master

add visible as an option for ace-jump-mode-scope
Keep the column the same when jump via line mode

Fix #50, which suggest to make column the same as before when jump
via line mode, this keep the line mode the same behavior as C-n/C-p.
Remove underline property for candidate key

Fix #48.
When original text has underline, the g and q candidate is different to distinguish.
So remove the underline display property explicitly to make candidate key clear.