Starting point for singlelineTextCtrl.

At this point in the project the control knows (i) how to determine the exact size
of the text it is to display, (ii) how to position the caret based on the sizing
specifications given at the top of the file. As it stands there is 1px of whitespace
between the top of the text and the top of the control, and 1px of whitespace between
the bottom of the text and the bottom of the control. The caret is the length of the
control. So if the 'exact' height of the text is 14px high, the caret is 16px high
as is the control.

The next step in designing the layout of the control is deciding how to implement a
border.
Added README
Merge branch 'master' of https://github.com/pazzer/wxSinglelineTextCtrl