MessageAction backwards compatibility

Adding WithToken to ISlackApiClient for using a different access token

Adding basic getting started documentation for Azure Functions

Adding Filter property to ConversationSelectMenu & ConversationMultiS…

…electMenu

Adding specific types for ViewInfo element values plus some missing B…

…lockAction types

Slash commands

resolves soxtoby#26

Forcing TLS 1.2 for websocket connections

Updating license date

Events example uses signing secret instead of legacy verifcation token

Merge pull request soxtoby#19 from mrmurb/use_post_for_chat.postMessage

WebApi: Changed HTTP methods to POST where recommended by Slack