Add g:session_save_color to toggle saving colorschemes.
Add g:session_save_color option variable in plugin/session.vim
Move the conditional check of g:session_save_color outside of the function
Add proper documentation for the g:session_save_color option
Fix a little typo
Use xolox#misc#cursorhold#register() to setup periodic callback
Merge pull request #78: Make color scheme persistence configurable

Related comments/issues/pull requests:
 - https://github.com/xolox/vim-session/issues/6#issuecomment-10604189
 - https://github.com/xolox/vim-session/pull/78
 - https://github.com/xolox/vim-session/issues/96