License update (Closes: #27):

 * Updated licensing headers as per assumption that the actual license is
   LGPL-3+ according to license text which did not match the headers.
   Used proper (L)GPL license statement and disclaimer.
 * Renamed "LICENSE.GPL3" to "LICENSE.LGPL3" to reflect the actual text of
   the license; moved unnecessary info to "README.md".
 * Removed unnecessary information from headers; kept only relevant
   copyright/license statement and backlink.
 * Explicitly mention that donation address is for Bitcoins
   to avoid confusion with other crypto-currencies.
 * Readme.md
   + included "intention statement" formerly used in headers.
   + mention donation address only once.
   + "normalised" email address.
   + mentioned BTC-E as well as MtGox; corrected some typos.