fix some denial of service attacks via hash

Ruby does not GC symbols so there is a possible attack where a large
hash could be passed in and symbolized causing memory bloat. If you are
using `strip: false` the attack is still possible so this is not a
complete solution.
add documentation about a possible security issue
Fix #165; fix RuboCop errors and pin version of RuboCop
oops, wrong version number
Merge branch 'master' into hash-dos
bump version to 1.1.3 and add CHANGELOG notes
fix accidental stringification of non-symbol keys
all filter names are Symbols
bump version to 1.1.4
the transform_keys method is only available in Rails 4.0.2+
bump version to 1.1.5
Use SVG badge URLs where available

Closes #150.
check for the needed modules rather than testing methods

Minitest changed how it works and broke this behavior. We can get away
with just checking to see if the needed modules are included/extended.
Update development dependencies
Update RuboCop configuration
Add UTF-8 comments
Fix #167; test multiple versions of ActiveModel
Merge branch 'master' into issue-36

Conflicts:
	lib/active_interaction/filters/hash_filter.rb
Extract error arguments into helper function
Avoid unnecessary assignment