Fix documentation for appendPartWithFileURL:name:error:.

The documentation said that the values for filename and the
Content-Type header was being obtained from a NSURLResponse,
but since this is a request, no response is available yet.

The documentation has been changed to reflect better where
those values really come from.
Add method to allow custom file name and content type for multiparts.

The previous method was selecting the file name and the MIME type
automatically depending on the given file URL.

The new method allows specifying a custom file name and a custom
MIME type for the those parts.
[Issue #837] Refactoring implementation of HTTP string encoding edge case to -responseStringEncoding to fix potential inconsistency in effective value
Rework delivery of AFNetworkingOperationDidStartNotification and AFNetworkingOperationDidFinishNotification to avoid crashes when logging in response to notifications
Set indentation settings to four spaces at the project level
Update network activity indicator only if requests have a non nil URL
Add asterisk (*) as a percent escaped character since it's in the reserved words per the RFC
Merge pull request #843 from blakewatters/bugfix/avoid-logging-crashes-from-notifications

Rework Notification Delivery to Avoid Crashes in Logging
Merge pull request #842 from 0xced/no-nil-network-activity

Update network activity indicator only if requests have a non nil URL
Merge pull request #841 from 0xced/indentation-settings

Set indentation settings to four spaces at the project level
The documentations states registered operation classes are consulted to the reverse order in which they are registered. New registrations are added to the beginning of the array in the register implementation. Fixed using the reverseObjectEnumerator when iterating the array which produced the opposite of documented behaviour. fixes #794
changed op_class variable to more objective-c style variable name operationClass
Merge pull request #849 from joelparsons/master

AFHTTPClient Registered operation classes consulted in wrong order.
Merge pull request #806 from drodriguez/gh-800-multipart-custom-filename

Add parts with custom file names and MIME types
Minor formatting fix
Minor formatting fixes
Merge pull request #844 from karbonworks/master

Add asterisk (*) as a percent escaped character...
UIImageView+AFNetworking not using setHTTPShouldHandleCookies

Signed-off-by: Mattt Thompson <m@mattt.me>