"Type :help for help", similar to ghci
auto merge of #6671 : kud1ing/rust/patch-1, r=z0w0
Implement static_assert attribute

This verifies that a static item evaluates to true, at compile time.
Add static_assert doc blurb
auto merge of #6670 : cmr/rust/static_assert, r=graydon

This verifies that a static item evaluates to true, at compile time.
Change how the input from rusti is formatted to allow duplicate definitions