Deprecate misc functions

[hadley]

• prepend
• rdunif
• rbernoulli
• when
• list_along

These don't seem obviously related to the core purpose of purrr, and have little CRAN usage.

[jdeboer]

I love the convenience of the rbernoulli function and hope to see it stay alive but moved to a more appropriate home.

[d-morrison]

I love the convenience of the rbernoulli function and hope to see it stay alive but moved to a more appropriate home.

seconded!