Normalize incoming emails (fix #59)

This is to prevent attackers from varying the case of their email
addresses to work-around rate-limiting.
Merge pull request #62 from fmarier/normalize-emails

Normalize incoming emails (fix #59)
Make the server executable
Merge pull request #65 from chilts/make-server-executable

Make the server executable
train-03
Avoid normalizing undefined email addresses
Validation errors should return 400 errors, not 500
Merge pull request #68 from fmarier/use_400_error_code

Use 400 error code for missing parameters
Remove redundant info
Document the code layout
Document the API
Document the current blocking and rate-limiting policies