Added .clang-format file

Added .clang-format to specify the code format for the project.
It relies on the tool clang-format. clang-format is not shipped
in xcode command line tools. To use clang-format inside xcode
download and install clangformat-xcode
https://github.com/travisjeffery/ClangFormat-Xcode

Updated contirbuting to add insturctions on setting up
xcode to use clang-format
Merge pull request #81 from cloudant/clang_format

Added .clang-format file
Allow setting certain HTTP headers for replication

Allows one to set optional HTTP headers for replication during the configuration
of an individual CDTPull/PushReplication object. This does not set these
headers globally.  The optional header property is found in the
CDTAbstractReplication class (which now conforms to NSCopying protocol).

Fixes a bug in TD_DatabaseManager.m that prevented headers to be set via
the 'properties' NSDictionary object used to create TDReplicator objects.

Adds tests for HTTP headers during replication

ReplicatorURLProtocol inherits from NSURLProtocol and is
used to gain access to all NSURLRequests made during replication.
This class passes the NSURLRequest to a delegate that tests the headers.
Merge pull request #80 from cloudant/36445-Expose-TDReplicator-requestHeaders

Adds ability to set optional HTTP headers in requests made during replication
Fixes test in ReplicationAcceptance.
Updates project files with newer version of Cocoapods.

These project files were updated by
1. pod install in Project/Tests/ReplicationAcceptance
2. Changing the Deployment Target to 10.10 and then back to
     original setting

The Tests/Podfile was updated as instructed by the cocoapods
command-line tool.
Merge pull request #83 from cloudant/fix-projects-with-latest-cocoapods

Updates project files as modified by newer version of Cocoapods.
Pin CocoaLumberjack version

Pin CocoaLumberjack version to 2.0.0-beta3 because 2.0.0-beta4 has removed
macros relied upon.
Prepare for 0.10.1
Creates individual threads for each TDReplicator.

This commit moves all of the threading code from TDReplicatorManager
to TDReplicator so that each TDReplicator executes on its own thread.

No tests are yet written to monitor simultaneous replications.
Fixes security issue where passwords were being sent to the log.
Adds test for multithreaded replication.

Two pull replications are executed simultaneously, pulling
from the same remote database to two different local databases.
A delegate captures updates from the replicators and determines
if the replicators were operating simultaneously.