Add expiration; Refactor a bit or alot
Update badge urls
Update package for repo transfer
Update for new git url
Update readme for new url
Use UTC time for travis
Rename postback to callback_url
Remove redundant test and rename
Don't use faketimer don't need it
Rename signed to sign
Change constructor name to Payload
secret is passed in at the point of signing; removes signature cache.
http_method renamed to method; not required as part of default minimum
Update readme with example
throw error when secret does not have a valid value
Update readme