Code and documentation update.

1.  Rewrote the input processing code section to ensure that all symbols
    are verified before historic stock data is requested, irrespective
    of the chosen Quandl data feed.
2.  Moved the REST request preparation code so that is is available for
    use in the new input processing code section.
3.  Added a local function to display the verified stock symbols so that
    the user may double check them if they so wish.