Merge pull request #95 from ckhatton/master

Fix issue #77 Home welcome view: Add missing </span> tags
Fix example session storage model in README
Don't attempt to retrieve session without session id

Retrieving session by nil successfully returns nil from
InMemorySessionStore, but when using AR model, Shop.find(nil) fails.

No need to lookup nil in the first place.
Remove trailing whitespace
Merge pull request #100 from vassilevsky/empty-session-shortcut

Do not attempt to retrieve a session from session store without an id
Merge pull request #99 from vassilevsky/retrieve-as-class-method

Fix example session storage model in README
Silently return nil for session when client supplies unknown session id
Merge pull request #101 from vassilevsky/handle-bad-session-id

Silently return nil for session when client supplies unknown session id
http -> https
set return_to on login_again_if_different_shop
Merge pull request #104 from Shopify/set_return_to_on_different_shop

Set return_to path on login_again_if_different_shop
Replacing the obsolete links

Using the Webarchive, I found that the new location for "http://www.shopify.com/developers/publishing" is "http://docs.shopify.com/partners/partner-resources/for-partners/building-a-shopify-app"
Also, the twitter account of https://twitter.com/shopifyapi is moved to https://twitter.com/shopifydevs
Merge pull request #107 from afshing/patch-1

Replacing the obsolete links
Fix issue #109 README.md: Incorrect Application Callback URL