RuboCop RSpec v1.0.rc1

• Update code to work with rubocop >= 0.19.
• Split UnitSpecNaming cop into RSpecDescribeClass, RSpecDescribeMethod and RSpecFileName and enabled them all by default.
• Add RSpecExampleWording cop to prevent to use of "should" at the beginning of the spec description.
• Fix RSpecFileName cop for non-class specs.
• Adapt RSpecFileName cop to common naming convention and skip spec with multiple top level describes.
• Add RSpecMultipleDescribes cop to check for multiple top level describes.
• Add RSpecDescribedClass cop to promote the use of described_class.
• Add RSpecInstanceVariable cop to check for the usage of instance variables.

WARNING: Cop names are under flux and will likely change in the near future.
We're hoping to introduce namespaces into the mix.