This needs to be fixed properly by removed the statusbar
manager and all uses.

Use the bounds from the logical highlight shape, rather than
calculating everything from scratch using the text metrics.

This doesn't help fix anything, but truncating everything to
integers is odd.

Issue #46

Fixes #62

When you select up to the end of the line, we now highlight the
remainder of the line. This means when a block of multiple lines
are selected, the highlight appears as a single contiguous
rectangle, rather than little bits and pieces.

No need to translate, we can just add some numbers together.

Use the proper font metrics to calculate line height and spacing.
For Dialog size 12 (our default font), this seems to be identical
behaviour. Other fonts define more sensible leadings, so are
spaced out properly.

This also fixes highlighting having gaps for large font sizes.

Change to using Rectangle2D.Float to avoid having to cast all
of the co-ords and dimensions to ints.

Remove a magic 1.5 in the calculations in favour of using the right
properties of the text.

Stop adding descents all over the place. This stops the highlight
rectangles being slightly offset and allowing descenders to peek
out.

Also adjust the initial Y offset to include padding, and increment
it in the right place.

We now always render bottom-to-top, regardless of whether lines
wrap. Previously for wrapped lines we jumped upwards, rendered
the wrapping lines top-to-bottom, then jumped upwards once more
and carried on bottom-to-top. That made for some really confusing
code.

TextPane no longer leaks memory like there's no tomorrow.
Selection works again.

I was wrong -- lineLayouts didn't need to be sorted. Making it
a TreeMap was quite expensive, as it had to do a bajillion
comparisons each time a line was added (which happens every
render cycle).

Remove some redundent checks, change firstChar/lastChar to be
relative to the current line, rather than within the whole
unwrapped line.