Prevent fatal error if no Tumblr connection exists. Shorten README.

git-svn-id: https://plugins.svn.wordpress.org/tumblr-crosspostr/trunk@848644 b8457f37-d9ea-0310-8a92-e5e31aec5664
Clarify: lack of theme Post Formats support means only Text posts work.

git-svn-id: https://plugins.svn.wordpress.org/tumblr-crosspostr/trunk@848652 b8457f37-d9ea-0310-8a92-e5e31aec5664
Fix typo in readme format.

git-svn-id: https://plugins.svn.wordpress.org/tumblr-crosspostr/trunk@848654 b8457f37-d9ea-0310-8a92-e5e31aec5664
Add FAQ about post formats, fix README heading format.

git-svn-id: https://plugins.svn.wordpress.org/tumblr-crosspostr/trunk@848655 b8457f37-d9ea-0310-8a92-e5e31aec5664