Log Message:
Update to 5.1:

Version 5.1
-----------

(bugfix release, released on 17th August 2015)

- Fix a bug in `pass_obj` that would accidentally pass the context too.

Version 5.0
-----------

(codename "tok tok", released on 16th August 2015)

- Removed various deprecated functionality.
- Atomic files now only accept the `w` mode.
- Change the usage part of help output for very long commands to wrap
  their arguments onto the next line, indented by 4 spaces.
- Fix a bug where return code and error messages were incorrect when
  using ``CliRunner``.
- added `get_current_context`.
- added a `meta` dictionary to the context which is shared across the
  linked list of contexts to allow click utilities to place state there.
- introduced `Context.scope`.
- The `echo` function is now threadsafe: It calls the `write` method of the
  underlying object only once.
- `prompt(hide_input=True)` now prints a newline on `^C`.
- Click will now warn if users are using ``unicode_literals``.
- Click will now ignore the ``PAGER`` environment variable if it is empty or
  contains only whitespace.
- The `click-contrib` GitHub organization was created.