Change time formating to use functions instead of methods.

This way the functions can be shared, instead of reimplemented all the time.
Fixes #35
Only use one set of templates.
gofmt

Sorry.  I need to add the commit hook on this machine.
Get the user in the transaction to prevent a datarace.

If the user adds two feeds at once, they could lose one feed.
Limit to 50 feeds.

Fixes #30
Report an error for an invalid feed URL.

Fixes #3