generic changes, process refactoring, `rotate` implementation and tests.
readme updated.
according to PR comment - fixed imports
- multi-line imports now uses `()` instead of `\`.
- fixed import groups by pep8.
- imports are sorted alphabetically.
according to PR comment - message for ArgumentsError is now more explanatory.
according to PR comment - removed unnecessary inline comment.
according to PR comment - operations on Image manipulates the internal stream + test.
Merge branch 'feat-implement-rotate-functionality' of https://github.com/dotpot/pilbox into dotpot-feat-implement-rotate-functionality

Conflicts:
	pilbox/app.py
Minor formatting changes
Resolved pep8 issues
More minor formatting changes
Integrated rotate pull request, added multi-operation support