Remove whitespace for effective at-mentions

If the display name contained whitespace, the function would keep the
whitespace in the at-mention.  According to observed behavior on the
website, this is not correct.

This commit removes all whitespace from the returned display name in the
appropriate function.
Streamline replying to comments

Append a single space after the at-mention in comment replies.
Add ability to copy link instead of visiting it
Merge pull request #98 from vermiculus/fix-at-mention-string

Fix at-mention string
Add months to sx-time-seconds-to-string

Fixes #102
Change months identifier
Merge pull request #99 from vermiculus/copy-visit-link

Add ability to copy link instead of visiting it
Preserve visual position when refreshing

Both for question list and question mode.
Give feedback on finished refresh.

Now that position is preserved, refreshing is so discreet that we need
some feedback. :)
Use let instead of letf

Older letfs are bugged.
Merge pull request #103 from vermiculus/add-month-time

Add months to sx-time-seconds-to-string
Merge pull request #104 from vermiculus/preseve-position-on-refresh

Preseve position on refresh
Fixes #92.  Change default filter from `'none` to `'(())`.
Merge pull request #106 from jleechpe/issue-92

Fixes #92.  Change default filter from `'none` to `'(())`.
Delete stack-exchange.el
Merge branch 'master' into issue-100