resolves #422
Inbox.ReceiveWhere() throws a NullReferenceException #427
Added missing using
Merge pull request #424 from Aaronontheweb/stashing-fix

Stashing Fix (resolves #422)
Merge pull request #428 from sibex/Inbox.ReceiveWhere-NullReferenceException-427

Inbox.ReceiveWhere() throws a NullReferenceException #427
Select wasn't copying and setting properties correctly
Adds a test that confirms bug #427
Merge pull request #430 from HCanber/test-for-bug-427

Adds a test that confirms bug #427
Supervise messages should be sent from self.

Init is called when Context hasn't been set, therefore we MUST always specify sender.
Merge pull request #418 from HCanber/supervise-from-self

Supervise messages should be sent from self.
Fixes two problems with how mailboxes are created

- If no mailbox has been specified, and stashing IS requested by the actor then a mailbox that supports bounded/unbounded stashing should be created.
- If no mailbox has been specified, and stashing is NOT requested by the actor, then the default mailbox as specified in the config should be used. The default mailbox in default config should be UnboundedMailbox.

This is what has changed
- In Mailboxes.GetMailboxType fallback to the default mailbox as defined in config, instead of "" (which defaults to UnboundedMailbox).
- Allow Props.Mailbox to return an empty string
- Default mailbox in pigeon.conf should be UnboundedMailbox and not ConcurrentQueueMailbox. Since UnboundedMailbox inherits ConcurrentQueueMailbox this will not have any effect on existing code.
Merge pull request #434 from HCanber/mailbox-stashing-fixes

Fixes two problems with how mailboxes are created
Update CONTRIBUTING.md