**Added:**

* Tab completers can now raise ``StopIteration`` to prevent consideration of
  remaining completers.
* Added tab completer for the ``completer`` alias.
* New ``Block`` and ``Functor`` context managers are now available as
  part of the ``xonsh.contexts`` module.
* ``Block`` provides support for turning a context body into a non-executing
  list of string lines. This is implmement via a syntax tree transformation.
  This is useful for creating remote execution tools that seek to prevent
  local execution.
* ``Functor`` is a subclass of the ``Block`` context manager that turns the
  block into a callable object.  The function object is available via the
  ``func()`` attribute.  However, the ``Functor`` instance is itself callable
  and will dispatch to ``func()``.
* New ``$VC_BRANCH_TIMEOUT`` environment variable is the time (in seconds)
  of how long to spend attempting each individual version control branch
  information command during ``$PROMPT`` formatting.  This allows for faster
  prompt resolution and faster startup times.
* New lazy methods added to CommandsCache allowing for testing and inspection
  without the possibility of recomputing the cache.
* ``!(command)`` is now usefully iterable, yielding lines of stdout
* Added XonshCalledProcessError, which includes the relevant CompletedCommand.
  Also handles differences between Py3.4 and 3.5 in CalledProcessError
* Tab completion of paths now includes zsh-style path expansion (subsequence
  matching), toggleable with ``$SUBSEQUENCE_PATH_COMPLETION``
* Tab completion of paths now includes "fuzzy" matches that are accurate to
  within a few characters, toggleable with ``$FUZZY_PATH_COMPLETION``
* Provide ``$XONSH_SOURCE`` for scripts in the environment variables pointing to
  the currently running script's path
* Arguments '+' and '-' for the ``fg`` command (job control)
* Provide ``$XONSH_SOURCE`` for scripts in the environment variables pointing to
  the currently running script's path
* ``!(command)`` is now usefully iterable, yielding lines of stdout
* Added XonshCalledProcessError, which includes the relevant CompletedCommand.
  Also handles differences between Py3.4 and 3.5 in CalledProcessError
* XonshError and XonshCalledProcessError are now in builtins

**Changed:**

* Functions in ``Execer`` now take ``transform`` kwarg instead of
  ``wrap_subproc``.
* Provide ``$XONSH_SOURCE`` for scripts in the environment variables pointing to
  the currently running script's path
* XonshError and XonshCalledProcessError are now in builtins

**Deprecated:** None


**Removed:**

* ``ensure_git()`` and ``ensure_hg()`` decorators removed.
* ``call_hg_command()`` function removed.


**Fixed:**

* Strip leading space in commands passed using the "-c" switch
* Fixed xonfig wizard failing on Windows due to colon in created filename.
* Ensured that the prompt_toolkit shell functions, even without a ``completer``
  attribute.
* Fixed crash resulting from malformed ``$PROMPT`` or ``$TITLE``.
* xonsh no longer backgrounds itself after every command on Cygwin.
* Fixed an issue about ``os.killpg()`` on Cygwin which caused xonsh to crash
  occasionally
* Fix crash on startup when Bash Windows Subsystem for Linux is on the Path.

**Security:** None