doc
Use 50 as default for config.trials
fix shrink for uint
update
Fix the tuple Shrink impl to be correct
fix shrink vec
cleanup
Use trials(50) for occurs
simplify arbitrary
lazy: Use &'static fn/extern fn for thunks.

It should be safe to use &'static fn as Owned function pointers. Mostly
safe. It's all until Rust supports either Owned &'static fn or extern fn
from closures directly.
lazy: Implement push_map, push_map_env with &'static fn and manual environment ptr
Update shrink for new lazy
qc: Remove unused trait bounds on quick_check
Add Arbitrary and Shrink for Result and Either and @T, @mut T, Cell<T>

HashMap & HashSet are not possible yet since they do not implement
Clone.
cleanup