API: /a/get_user_info
API /a/login
Update /a/login

Login by email only
Updates
Update api.md
Update api.md
Update api.md
Update api.md
Update api.md
Merge pull request #15 from charliezhang/master

Some login/signup APIs
Merge pull request #13 from roba269/master

Add a toy user signup/login, and session support
Add encoder from json to datastore entity
Rename "server" directory to "tools"