assets/styles.css: Fix header comment grammar
assets/impress.js: Tidy up file header

Give proper attribution to Bartek Szopka but state that this is a
modified version of the file.
assets/impress.js: Change indentation level to 2 spaces
assets/impress.js: Tidy code style
assets/impress.js: Use the modulus operator in prev/next
assets/impress.js: Add a functioning modulus operator

In JavaScript:

    -1 % 5 = -1

With the modulus operator:

    -1.mod(5) = 4
assets/impress.js: Add support for nonsteps

This allows you to add a .nonstep class to steps, which prevents them
from being selected by the next() or prev() functions. For example:

      <div id="a" class="step"></div>
      <div id="b" class="step"></div>
      <div id="c" class="step nonstep"></div>
      <div id="d" class="step"></div>
      <div id="e" class="step"></div>
      <div id="f" class="step nonstep"></div>

Cycling through the steps will produce the order a, b, d, e, a, b, d...
Steps c and f will be omitted. You may still navigate to these nonsteps
by calling the impress_goto() function, or by navigating to the #/<id>
URL.
assets/impress.js: Add `impress-on-nonstep' class

This class is added to the document body class list when a nonstep step
is entered, and is removed upon returning to a normal step.
Add support for right arrow on nonstep

When on an nonstep, the right arrow acts as a return-to-overview button,
and the left arrow is hidden.
Replace the static license page with a nonstep

This integrates the license page into the home impress presentation.
Replace the static privacy page with a nonstep
index: Add a link to how to disable cookies

And a bit snarky, but whatever ;-)
Combine License and Source sections

Adds a unified `Source Code' nonstep which details where to obtain the
source, and the License used to distribute it.
index: Rough fix for success message styling
Merge branch 'impress'