Create cider-doc-map and add "\C" versions of the keys when it makes sense.

Very nice initiative to create a doc map. Thanks. 

This patch adds a couple of control prefixed keys. For my brain <kbd>C-c C-d C-d</kbd> is much more convenient than <kbd>C-c C-d d</kbd>.
That's not correct - this very same command show both clojure and java documentation. The different with the javadoc command is that `cider-doc` displays the documentation in a `cider-doc-mode` buffer and `cider-javadoc` opens a javadoc url in the default browser.