Clapautius - changes in rtags.el

* add support for unsaved files (reparse file if it's modified since last parsing - sync operation)
* implement rtags-display-summary - function to display a short description of an element in a tooltip
* rtags-show-target-in-other-window now has optional parameters to use existing windows and not break the window layout;
* rtags-taglist - can use existing window; changed appearance;