Add unfurl web API action

Adds the unfurl action from the Slack Web API

Modify certain web functions to support Slack BlockKit

Merge pull request #226 from juanazam/add_missing_blocks_arg_to_chat_…

…calls

Add missing blocks optional argument to chat endpoints

Fix crash of put_in/update_in

Merge pull request #224 from entertainyou/master

Fix crash of put_in/update_in

Fix default state

Patch fix for default state bug

Add conversations.invite web API method

Merge pull request #222 from BlakeWilliams/acc-add-conversations-invite

Add conversations.invite web API method

Add conversations.create web API method

Merge pull request #221 from BlakeWilliams/acc-add-conversations-create

Add conversations.create web API method

Swap Poison for Jason

Merge pull request #219 from BlakeWilliams/acc-upgrade-jason

[IMPORTANT] Swap Jason for Poison

Support for Elixir 1.7-1.10

Merge pull request #217 from BlakeWilliams/acc-upgrade-elixir

Upgrade Elixir to support 1.7.2 through 1.10.1

Fix hex plugins to make publishing work

Downgrade ex_doc to ~> 0.18 to allow hex.publish on Elixir 1.6

Adds API methods, fixes charset warnings

Adds missing Slack Web API methods:

• admin.apps.*
• app.uninstall
• auth.revoke
• chat.scheduleMessage
• oauth.v2.access
• users.profile.get
• users.profile.set
• views.*

Fixes messaging warnings

superfluous_charset warnings thrown with every im.open call are now properly handled with a default Content-Type of utf-8 (it was missing).