Artists exhibiting their wares at this weekend's Paradise City Arts Festival have been generous with items for the event's silent charity auction, according to Founding Director Linda Post.  She says hundreds of donations have been given by artists to be auctioned off this year, to benefit the Dakin Pioneer Valley Humane Society.  Post says the silent auctions have raised about $300,000 for charities over 17 years.  The festival runs Saturday through Monday at the Three County Fairgrounds in Northampton.