Update README
Update code for demonstrating progress
Add section 'Finally'
Update README.md

Merge the table 'Progress meaning' to the table for aggregate methods
Update README.md

Add section 'Cancel'
Add test code for README.Cancel
Merge branch 'README' of https://github.com/coppercash/IPromise into README
Merge branch 'README' into develop
Merge branch 'develop'