Merge pull request #26 from spderosso/master

some fixes
Addressed some of the reviewers' comments
Merge branch 'master' of https://github.com/eskang/500lines

Conflicts:
	same-origin-policy/doc/chapter.md
- Added explanation of calls
- Renamed 'before' and 'after' in 'Call' signature as 'start' and 'end'
first cut at some of the SOP relaxations