2015-05-24 io.js v2.1.0 Release

PR-URL: https://github.com/nodejs/io.js/pull/1777

Notable Changes:

* crypto: Diffie-Hellman key exchange (DHE) parameters ('dhparams') must now be
  1024 bits or longer or an error will be thrown. A warning will also be printed
  to the console if you supply less than 2048 bits. See https://weakdh.org/ for
  further context on this security concern. (Shigeki Ohtsu) #1739.
* node: A new --trace-sync-io command line flag will print a warning and a stack
  trace whenever a synchronous API is used. This can be used to track down
  synchronous calls that may be slowing down an application.
  (Trevor Norris) #1707.
* node: To allow for chaining of methods, the setTimeout(), setKeepAlive(),
  setNoDelay(), ref() and unref() methods used in 'net', 'dgram', 'http',
  'https' and 'tls' now return the current instance instead of undefined
  (Roman Reiss & Evan Lucas) #1699 #1768 #1779.
* npm: Upgraded to v2.10.1, release notes can be found in
  https://github.com/npm/npm/releases/tag/v2.10.1 and
  https://github.com/npm/npm/releases/tag/v2.10.0.
* util: A significant speed-up (in the order of 35%) for the common-case of a
  single string argument to util.format(), used by console.log()
  (Сковорода Никита Андреевич) #1749.