Use kramdown instead of redcarpet

Redcarpet needs C-extensions enabled on jRuby which isn't enabled by
default. Kramdown is pure ruby and works on all Ruby versions
Don't allow failures on jRuby anymore
Merge pull request #1 from rmehner/jruby_support

Jruby support
fix rbx testing (fixes #2)
sidekiq 3 compatibility

fixes #5
0.2.0
Added the ability to encrypt specific arguments or nested values
Ignore .project files
Removed pry
Added metadata to indicate if a value is wrapped (backwards-compatibility)
Fixed test to use worker class for client argument
Handle worker class as string
Check for encrypted value after deserializing
Removed unused `@note`