Added rudimentary help dialogue

The help dialogue is in the form of a pop-up with text informing the
player how to play the game. When the link is clicked, the showHelp
function is called. The function creates the div and text elements and
controls the display of the pop-up.
Removed variable declaration playButton

It is unnecessary to declare a variable that stores a reference to an
HTML element if it is only used once. The playButton variable was
referred to only once: to set the display property of the play button
to none. Thus the variable was removed in favor for calling the
getElementById method together with setting the display property, in
a single statement.
Replaced links with buttons

The anchor tags were replaced with button elements. The showHelp
function is called from the button with the onclick property, from
inside the startGame function. Buttons are more suitable in this case
since they are displaying (or toggling) pop-ups, not redirecting to
another page. Using the onclick property rather than a link with
href:javascript is more consistent with the unobtrusive javascript
approach.
Added help access before game starts

The player should be able to view the help, about, and options before
initiating the game.

To add this functionality, the onclick property of the help button
which fires the showHelp function was moved from inside the startGame
function into global scope. showHelp was also moved from startGame into
global scope.

This is a quick-and-dirty implementation. This should probably be
changed for better methods such as self executing functions, AMD, module
pattern, namespaces, closures, etc.
Fixed multiple help dialogue creation

The showHelp function fired by the help button was creating multiple
help divs in the DOM instead of only creating one and hiding and
displaying it. Since the expression of the if statement was testing if
the variable help is undefined, control never followed the else
statement because each time the showHelp function is called, the help
variable is created anew. (ie local variables as they pertain to
function scope)

This was fixed by checking instead for the creation of the help div in
the DOM using the getElementById method.
Fixed tokens covering up help dialogue

When the help button is clicked before the play button, the
help div is added before the token elements on the DOM list, which
causes the tokens to cover up the help dialogue when the help button is
clicked later during the game.

This was fixed by specifying the z-index properties of the token and
help classes to 0 and 1 respectively.
Added toggling of help dialogue with help button

Players can now hide the help dialogue by clicking the help button
again
Replaced text in buttons with icons
Added button icon acknowledgements to README
Removed about button

Having two buttons with a question mark and the letter 'i' is somewhat
ambiguous, so the about 'i' button has been removed. This allows for a
simpler interface with only help and options buttons. The information
that was meant to be in the about menu can be added to the help menu.
Moved the help menu as a child of play-area

All the HTML elements that are a part of the game should be added as
children of play-area to contain and separate them from other web page
elements when the game is deployed on a website.

The change introduces a graphical layering error similar to the one
resolved in commit a215, where the tokens are displayed above the help
menu. This is most likely caused because the help menu and the tokens no
longer share the same parents, thus the z-index properties between the
two no longer apply.

Also added dark gray background color to body of nim.html to reduce eye
strain for development purposes.
Moved tokens as children of play-area

All token objects are structured in the DOM as children of the play-area
div.

The help menu display error from the previous commit has been fixed. It
was caused by two different issues: 1) The help menu shape would appear
distorted after closing and reopening it, and 2) The tokens would cover
up the help menu. The first issue was fixed by using the visibility
property instead of display. The second was fixed by setting the
position property of the help menu to relative, since the position
must be set to absolute, relative, or fixed for the z-index to work.
Added OK button to help menu

Needed to set display property of the button to block so that it would
center properly with auto left and right margins.
Added note files and unused images to repo