File-deletion on Case-Insensitive filesystem when title note capitalization changes

[matteoquintiliani]

On a Case-Insensitive filesystem, such as Mac OS X, a note is deleted if its title capitalization changes.

For example, renaming the title's note from "hello" to "Hello", the note is deleted.

I think the problem depend on the fact that function xolox#notes#save(), when the title changes, it copies the new note and then deletes the old one, instead of actually renaming.

An useful comment I found could be at https://github.com/xolox/vim-notes/blob/master/autoload/xolox/notes.vim#L421