Replaces occurrences of `AFHTTPSerializer`

Changes some comments where either AFHTTPRequestSerializer or
AFHTTPResponseSerializer should be user insted of AFHTTPSerializer
Finalizing #1412 by fixing __IPHONE_OS_VERSION_MIN_REQUIRED to __IPHONE_OS_VERSION_MAX_ALLOWED in `AFHTTPSessionManager` too ( #1412 only did it in `AFURLSessionManager` )
Merge pull request #1486 from AliSoftware/master

Finalizing #1412 fix for __IPHONE_OS_VERSION_MIN_REQUIRED
Merge pull request #1485 from brunokoga/master

Replaces occurrences of `AFHTTPSerializer`
s/an/a/
allow init and initWithConfig work with session mgr
Fixing behavior if response is `nil`

Testing without internet connection, `operation.response` is `nil` and the `failure` block is not called. We can get the URL from the `operation.request` instead of `operation.response` (as done in the `success` block).
Merge pull request #1500 from jchambers/trivial_doc_typo_fix

Fixed a very minor typo in the docs
Replacing string literals in NSCoding with NSStringFromSelector(@selector()) pattern
aCoder / aDecoder -> coder / decoder
[Issue #1517] Fix implementation of batchOfRequestOperations:progressBlock:completionBlock: for nil when passed empty operations parameter
Merge pull request #1505 from marcelofabri/patch-1

[2.0] Fixing behavior if response is `nil`
Merge pull request #1503 from subdigital/session-manager-initializers

Allow init and initWithSessionConfiguration: to work with AFHTTPSessionManager
Use AFHTTPResponseSerializer for AFHTTPRequestOperation
Remove the executable permission from .m files
[Issue #1525] Removing duplicate conditional
Merge branch 'master' of github.com:AFNetworking/AFNetworking
[Issue #1531] Adding more explicit data / MIME type / text encoding name version of UIWebView -loadRequest:...
Merge pull request #1526 from techee/master

Use AFHTTPResponseSerializer for AFHTTPRequestOperation
[Issue #1526] Updating documentation for default response serializer of AFHTTPRequestOperation