fix #97

Hightlightthickness is 0 means the Text widget will not show the highlight border and I agree this, because the border looks ugly.

And here is a screenshot that shows the difference between borderwidth=2 and the normal borderwidth, there are 1px black frame in the left and 2px grey frame in the bottom, so I disagree the second.

And the relief, here is the screenshot (test with borderwidth=2):

I think normal relief is better than the solid, so I think they can set the solid by themself.

So we just need set the highlightthickness=0 as default.
(Of course this is just my option, maybe we can ask Akuli for options.)