Minor update to readme
Create test for Message class
Initial implementation of Message class
Create initialiser for the testsuite
Create config file for phpunit
Add vendors dir to gitignore
Composer config and lock files
Change test name for json test
Add phpunit.xml to gitignore
Added Guzzle to composer.json and updated
Replace Message class as an interface

Change Message class to be an interface outlining what Slack messages
should look like. The old "Message" class will change to CustomMessage
and implement this interface
Reorder methods to match interface
New test for constructor of CustomMessage
Fix typo in test string for constructor
Test that asJson returns minimum viable json for slack
Remove text method from Message interface

Test property will be set via the constructor arg as it is the only
required piece of data in Slack's API
Tests to ensure that the optional params work

Slack exposes a small selection of optional params the JSON can contain
to enhance the message. These tests ensure that the setter methods for
these params cause the correct JSON to be generated
Implement setter methods for optional params
Initial travis setup
Set up new test for Pslackr constructor