It looks like this is the basic setup:
https://twitter.com/intent/tweet?
url=<url to tweet>
text=<text to tweet>
hashtags=<comma separated list of hashtags, with no # on them>
This would pre-built a tweet of: <text> <url> <hashtags>
The above example would be:
https://twitter.com/intent/tweet?url=http://www.example.com&text=I+am+eating+branston+pickel+right+now&hashtags=bransonpickel,pickles
There used to be a bug with the hashtags parameter… it only showed the first n-1 hashtags. Currently this is fixed.