Update modules/buster-assertions.rst
Update modules/buster-assertions.rst
Update modules/buster-assertions.rst
Update modules/buster-assertions.rst
Update modules/buster-assertions.rst
Update modules/buster-assertions.rst
Update modules/buster-assertions.rst

Description of the assertions completed and overview for assertions added.
Update modules/buster-assertions.rst

Description of stubs and spies completed.
Merge pull request #12 from dwittner/patch-1

Documentation of the buster assertions completed