Add assertDoesntExist method

[jackbayliss]

This adds an assertDoesntExist method, as I often find myself having to do assertElement just to check that something isn't actually there. This is similar to assertContainsElement but just a quick way of checking something isnt there.

This can also be chained with assertContainsElement easily- due to sharing the same parser.

Changes

• Adds assertDoesntExist
• Updates all the Macros / ide helpers
• Adds to the readme
• Added tests to prove its functionality ( I will probably come back and add more tests later on)

[sinnbeck]

Exelent. Sounds like a good idea