Fixed a tooltip bug in < IE9

Fixed a bug where the tooltip was moving to an empty selection,
generally done when clicking out of the current selection in browsers
that don't support getSelection()
Added in text variable storage in < IE9
Added in callback

Added in a callback function, removed the textVariable from methods. The
callback is passed the text selected. Also adjusted the tooltip bug fix
in < IE9 to just obey the minWords setting.
Updating the readme
Readme styling
Update README.md
Merge pull request #3 from GYatesIII/save-selection-text

Added in callback function and increased older browser support