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>.
Sorry, I didn't understand this one. Do you want to remove the whole keymap or just to leave "j" bound to `cider-doc-javadoc`? If the latter than it is bound to "J" now and the `cider-javadoc` is bound to "j".