Add seec::toUnicodeString(), which converts a wxString to an ICU UnicodeString.
Start working on issue #42 by storing annotations on the SourceFilePanel, so
that we will be able to re-render them when a resize event occurs. We still
need to implement the column alignment, a method that causes all annotated
lines to be re-rendered, and then wire up the resize event handler.
Rerender annotations when resizing (closes #42). Also implement indentation
for non-wrapped annotations, set annotation styles on a per-char basis so that
multiple annotations with different styles can be used on a single line, and
merge annotateLineWrapped() into annotateLine().