fix #1294 -- add `nikola new_* -e`

Signed-off-by: Chris “Kwpolska” Warrick <kwpolska@gmail.com>
more sensible error message

Signed-off-by: Chris “Kwpolska” Warrick <kwpolska@gmail.com>
changelog for #1294

Signed-off-by: Chris “Kwpolska” Warrick <kwpolska@gmail.com>
Merge pull request #1296 from getnikola/edit-on-new

fix #1294 -- add `nikola new_* -e` (run editor from new_post)

Great! Thanks, @Kwpolska.