Add minibuffer check to `evil-execute-in-emacs-state'

Don't return to Normal state if currently in the minibuffer.
This prevents an error if the user goes from Normal state to
Insert state for the duration of one command and then enters
the minibuffer while in Insert state.
Comments cleanup

Improve the wording of some docstrings.
Simplify `evil-insert-resume'

Define `evil-insert-resume' in terms of `evil-goto-mark'. Add a
NOERROR argument to `evil-goto-mark' to let "gi" degrade to "i"
if entering Insert state for the first time.
Fix auto-indenting of "o"/"O"

Some Emacs modes may offer an incomplete indentation implementation.
If `indent-according-to-mode' signals an error, it prevents
`evil-open-above' and `evil-open-below' from entering Insert state.
Reorder the code so that Insert state is entered first.