add very basic .gitignore
SECURITY: validate exchanged ephemeral keys

Fixes iSECs Finding #14
update Readme to reflect insecurity in versions < 0.2.1
bump version to 0.2.1
update srp_js in the example to use new repository and files
fix tests to use hex interface to session
add Gemfile and include activesupport in gemspec

It was not available on travis before
Merge pull request #2 from azul/security/validate_ephemeral_values

Security: validate ephemeral values