Merge pull request #761 from vitoshka/jump-to-var

`cider-jump-to-var` is broken when there is no symbol at point
Fix "making delay-mode-hooks buffer-local" message
Merge pull request #764 from vitoshka/delay-mode-hooks

Fix "making delay-mode-hooks buffer-local" message
Add a basic Java classpath browser
Add namespace browser

Extend CIDER documentation support to include a namespace browser.
`cider-browse-ns` will list all vars in a single ns.
`cider-browse-ns-all` will list all currently loaded namespaces.

Uses `cider-doc` to show documentation.
Merge pull request #765 from jxa/browse-ns

Add namespace browser
Mention namespace browser in the changelog
Add command cider-open-classpath-entry
Use defvar-local
Derive from special-mode
Enhance `cider-find-file` and use stacktrace file data for navigation