Merge pull request #445 from krisajenkins/pprint-defun

Adding cider-pprint-eval-defun-at-point.
Bump dash.el dep to 2.4.1
Add the ability to use a configurable result prefix in the REPL
Colorize result prefix in the REPL
Use defvar-local to define buffer-local variables
Add missing default values
Add some basic help to the REPL shortcuts
Tidying up switch-to-relevant-buffer, updating docs, and adding check against ambiguous switch.