devserver: display documentation for exposed methods
devserver: display documentation for exposed methods

* A new doc/<method> URL for displaying the docstring of various exposed
  devserver methods.

* The index page lists all available methods, and clicking them jumps to
  their respective doc page.

* Added/fixed docstrings of some exposed methods.

BUG=None
TEST=List of methods displayed, documentation displayed; unit tests pass

Change-Id: Ib13ce8f4ec70bf99688ea40aa156822035422d8c
Reviewed-on: https://gerrit.chromium.org/gerrit/33893
Commit-Ready: Gilad Arnold <a0dab390cfdc583218cee97b60c5c4eb1be355d2@chromium.org>
Reviewed-by: Gilad Arnold <a0dab390cfdc583218cee97b60c5c4eb1be355d2@chromium.org>
Tested-by: Gilad Arnold <a0dab390cfdc583218cee97b60c5c4eb1be355d2@chromium.org>

marineam/coreos-dev-util,coreos/dev-util,mgireesh05/dev-util,mgireesh05/dev-util,coreos/dev-util,mgireesh05/dev-util,coreos/dev-util,marineam/coreos-dev-util