Preview Pull For Mining Guide

Created this to help keep track of work being done before the pull request against the main bitcoin.org repository.  Feedback both here and on the mailing list is welcome.

**Warning:** the commits shown on this pull will be squashed down to one commit per author for the real pull.
@harding Sorry, I've commented on a previous commit. Here's the same feedback again. In order to execute the function as soon as the value is changed instead of when the user leaves the input box, you may want to use :

    onpropertychange="calculate_todays_terms(event);" oninput="calculate_todays_terms(event);" onkeypress="calculate_todays_terms(event);"

Then use:

    function calculate_todays_terms(e) {
      if(e.type=='propertychange'&&window.event.propertyName!='value')return;

to prevent IE from executing the function except when the value of the input box is changed.

Note: "onchange" works just fine for select boxes, since the user doesn't type any information.