Add Link Names

• Add LinkNames parameter, for enabling @-tagging of users without having to know their slack userid.

Add mocks for interfaces

Merge pull request #3 from twiebe-va/add-mocks

Add mocks to interfaces

Fix method name `SetIncomingWebhookURI`

Merge pull request #2 from twiebe-va/fix-method-name

Fix method name in interface

Implement SendAsync

Merge pull request #1 from twiebe-va/implement-send-async

Implement SendAsync

VSlack-go v1.0.0

Version 1.0.0 of VSlack for golang.