Add package `imenu-anywhere'
Fix smartparens settings

* Call `sp-use-paredit-bindings' to let smartparens set paredit bindings.
* Fix extra closing pair is inserted and then deleted immediately.  Set
  blink-matching-paren to nil is the key to fix this.
* Remove package `paredit-everywhere' since smartparens supersedes it.
Use package `webjump' to search sites

Also add some useful sites such as Github, Stack Overflow, etc.