This make `SPC h SPC` as default binding for accessing `helm-spacemacs`,
by either A) changing all the documentation; and B) adding a deprecation
message for `SPC f e h`.
The deprecation use a warning, because if a message is used it's hidden
directly when the helm buffer is shown, making it nearly unnoticeable
for the user.
In *spacemacs* buffer, the quick help in `[?]` shows that `m` jumps to
the menu. However, if one customizes the startup lists by setting
`dotspacemacs-startup-lists '(recents bookmarks projects)`, the shortcut
`m` of jumping to the menu would be shadowed and `m` jumps to Bookmarks.
With the help of travisbhartwell and TheBB, I changed the shortcut of
jumping to the Bookmarks to `a` to avoid this shortcut conflict.
