Adjust horizontal location for left position and vertical location for target rectangle
Fix location of rectangle for left position
Use 'x' and 'y' rather than 'dx' and 'dy' for text box

 - Fixes text alignment problem in Firefox; still works in Safari and Chrome
For text box, change alignment-baseline to dominant-baseline

  - Fixes the vertical alignment in Firefox (which seems to ignore
    alignment-baseline)

  - Still works in Safari and Chrome on Mac
Adjust placement when target object is a rectangle
Fix placement of tip for left/right orientation

  - Calculations were complicated and not-quite-right
Merge pull request #4 from kbroman/master

Fix alignment for left position