More slides splits and image overlays

[robertodr]

This adds some more slide splits with different percentage of space per column.
The following creates a 50-50 split of the slides with two columns:

---
layout: false
class: split-50
## The Problem of Solvation

.column[
Something
]
.column[
Something else
]

Available splits are: 30-70, 40-60, 50-50, 60-40 and 70-30

Moreover, image overlays are also possible, albeit with explicit HTML syntax:

<div class="imageWrapper">
  <img class="overlayImage" src="images/spherical_diffuse.jpg" style="width: 80%" align="middle">
--
  <img class="overlayImage" src="images/paper.png" style="width: 110%" align="middle">
</div>
<p style="clear: both;">

[bast]

Thanks! I will test this very soon on my side and then integrate.

[bast]

No time to test now but I trust you with this :-)

[robertodr]

I've used them both on a couple of slide decks this for example

[bast]

Looks good :-)

[bast]

I wonder whether it would be more intuitive to call them e.g. split-70-30 - or does it look redundant? I am worried here about backwards compatibility of the naming. The functionality is great.

[robertodr]

Yes, of course! Rename as you see fit. I agree that the names are not immediate.

[bast]

Renamed in ec56766.