Use SHA1 for default #retry_identifier
Match exception instance against retry_exceptions

This allows to 'tag' exceptions with a module instead of having to
wrap them in custom exception classes, which is useful when you want
to keep the original exception for logging and diagnosis after the
retry limit was exceeded. Using the === operator makes the matching
work the same as the ruby rescue clause.

Example:

module TransientError; end

def foo
  ...
rescue Timeout::Error => e
  raise e.extend(TransientError)
end

class SomeJob
  def self.retry_exceptions
    [TransientError]
  end
  ...
end

The old behaviour of the public method retry_exception? so that you
can alternatively pass an exception class instead of an exception
instance to it is kept but documented as deprecated.

This is a reworked version of this commit:

https://github.com/til/resque-retry/commit/cfa397048430ed437c91abffeb4659f59d48ac15
Update HISTORY.md with @til's changes.
Cutting v1.0.0 for public release.
Merge pull request #48 from d11wtq/sha1-retry-identifier

Use SHA1 for default #retry_identifier
Update README.md

Add dependancies status badge (all green, congrats!).
Thanks
pin minitest to version 4 so the tests will run
ignore stdout file created in tests
remove deprecated redis 'glueoutputbuf' option
fix mocha include warning
add .ruby-version file
require resque >=  1.25
remove dependence on Resque::Helpers
use https rubygems source
Merge pull request #86 from teeparham/fix_tests

Fix tests
Merge pull request #87 from teeparham/resque125

Remove dependence on Resque::Helpers, require resque 1.25
Change rubies travis-ci.org tests against.
Merge pull request #88 from teeparham/rubygems_source

use https rubygems source
Drop 1.9.2 from travis-ci.org builds, remove devel dependencies no-longer needed.
Merge pull request #75 from gravis/patch-1

Update README.md to include Gemnasium badge.