data.Opml is sometimes null, so set to []
Use the standard charset reader
Refactor into smaller functions
Convert feed body to UTF-8

fixes #308
Use correct content type

fixes funky char errors report on twitter
Use UTF-8 as a default if it's valid

For feeds that do not identify charset (jvns.ca, for example), the charmap
package defaults to Windows1252 if there is no byte that appears to be in
UTF-8's range in the first 1024 bytes. But if the entire file appears to be
UTF-8, let's just use that.
Check for the UTF-8 xml header before decoding

For feeds without a charset in the content type, this allows them to also
identify their charset via the xml header. We could remove the previous
commit in lieu of this, but the Windows 1252 default is still bad, and
would have gotten triggered if, say, the newline at the end of xml.Header
didn't appear in the xml file.
Update to new go repo locations
goimports
Add a charset decoder

fixes #310
Don't double-decode XML
escape key also hide messages
#305 Many favicons are only available via HTTP, so leave the URL alone.

Test case: http://www.sheldoncomics.com/index.xml
Actual favicon http://www.sheldoncomics.com/favicon.ico
Requests to https://www.sheldoncomics.com/favicon.ico time out.
#313 show message when user submits bad OPML

This moves the initial XML parsing into the form submit request,
then stores the resulting Opml object as a gob
instead of storing the raw upload bytes.
If the upload is malformed, the request response body
includes a copy of the full error message.
The ajaxform code will show this to the user as a new message.

There may be some risk in moving work into the main request,
because appengine likes requests to be low-latency.
I think it's a reasonable tradeoff, in part because
imports are relatively infrequest.
Merge pull request #315 from mblakele/esc-for-messages

escape key also hide messages
Merge pull request #316 from mblakele/305-favicons

#305 Many favicons are only available via HTTP, so leave the URL alone.
cleanup per code review
Merge pull request #318 from mblakele/313-bad-opml

#313 show message when user submits bad OPML
Display error on feed too large

fixes #322
gofmt