.Net 4.0 support for Serilog.Sinks.ElasticSearch

Serilog.Sinks.ElasticSearch .Net 4.0 distribution is added to solution.
Serilog.Sinks.Seq package.config file was missing in the main
repositories, so its added.
A simple exponential backoff mechanism for PeriodicBatchingSink
Forgotten project file is added
minor - fix whitespace
Ensure that row key is unique by appending an incrementing index. Fixes #225
Merge branch 'Net-4.0-support-for-Serilog.Sinks.ElasticSearch' of https://github.com/cihanduruer/serilog into cihanduruer-Net-4.0-support-for-Serilog.Sinks.ElasticSearch
By convention we keep packages.config files pointing to .NET 4.5.
Merge branch 'cihanduruer-Net-4.0-support-for-Serilog.Sinks.ElasticSearch'
increment rowkeyindex as an atomic operation
Maximum 10-minute backoff interval rather than 15, just to be on the "safer" side.
.NET 4.0 build support for new batching back-off strategy.
Merge pull request #226 from joshka/ensure-tablestorage-rowkey-unique

Ensure Azure Tablestorage rowkey is unique
Merge branch 'master' into feature-206-batching

Conflicts:
	src/Serilog.Sinks.AzureTableStorage/Sinks/AzureTableStorage/AzureBatchingTableStorageSink.cs
Merge branch 'feature-206-batching'
Changelist.