Previously, if alwaysDo was used and the user wanted to generate
one or more additional snippets when calling perform a separate call
to `snippets` was made prior to calling `perform`. This had two
problems:
- it required the result handler to be stateful (see gh-243)
- it wasn't clear that the additional snippets would be produced when
a subsequent call to perform was made
This commit introduces a new API that allows the additional snippets
to be specified within the MockMvc call. The old API has been
deprecated and will be removed in 2.0.
Closes gh-249
42353a0b5f