Store helper proxies instead of raw view contexts

Closes #436.
Improve helper method performance
Define proxy using `send` instead of `delegate`

Rails 4 will not delegate non-public methods
Unlock JRuby SQLite dependency
Merge pull request #438 from haines/issue_436

Store helper proxies instead of raw view contexts
restrict inclusion of test dependencies to test environment only
Improve Devise integration
Remove `stub` from Devise helper

Closes #439
Merge pull request #440 from haines/devise

Improve Devise integration
tagging 1.1.0
add license information to gemspec

so that it can be used from rubygems.org API
Merge pull request #441 from jordimassaguerpla/master

add license information to the gemspec
Merge pull request #442 from FM-Systems/restrict_test_dependencies

restrict inclusion of test dependencies to test environment only
Update CHANGELOG for v1.1.0

[ci skip]
Only return attributes implemented by the decorator

Closes #444
Add serializers
Merge pull request #448 from haines/attributes

Improve decorator serialization
Fix failing specs