Escape multibyte line terminators in JSON encoding

Currently, json/encoding respects the JSON spec (as it should) which 
disallows \n and \r inside strings, escaping them as expected.

Unfortunately, ECMA-262 (Javascript) disallows not only \n and \r in 
strings, but "Line Terminators" which includes U+2028 and U+2029. 
See here: http://bclary.com/2004/11/07/#a-7.3

This pull request adds U+2028 and U+2029 to be escaped.

# Why? 

It's very common to see something like this in a Rails template:

<script type="text/javascript"> 
var posts = <%= @posts.to_json %>;
</script>

If U+2028 or U+2029 are part of any attributes output in the to_json
call, you will end up with an exception.
In Chrome: Uncaught SyntaxError: Unexpected token ILLEGAL 

# Why not?

This is JSON encoding, and the JSON spec is specific about how to 
encode strings. U+2028 and U+2029 don't get special treatment.

Just trying to start a discussion... what do you do in your apps
to deal with this? Is there a convention I'm missing?
fix HashWithIndifferentAccess#to_hash behaviour
Rails 4 has deprecated :order in has_many to use a lambda instead, update the guide accordingly
Fix typo "can exploited" with "can be exploited"
Add a few overview bullet points
Clean up the wording in a few places
document String#to_time exception
fix typo
Simple grammar updates
added to rdoc for unscope that default_scope wins
Capitalizing internet to Internet. [ci skip]
replace apostrophe with backquote for matching [ci skip]
Add some documentation for AM.mailer_name
Fix incorrect post_path link generation.
Remove unopened closing brace.
Fix another incorrect post_path link generation.
Update CreateComments migration to reflect the output from Rails 4.
comments in the callbacks description are in present tense
Changing the wordings in a few places
dir -> directory