Make std.file.mkdir safe
Use std.windows.syserror.wenforce instead of cenforce on Windows
Fix the documentation for mkdir
use sum instead of reduce in example code
Merge pull request #2590 from MartinNowak/docs

use sum instead of reduce in example code
Merge pull request #2560 from tom-tan/safe-file-mkdir

Make std.file.mkdir safe
fix datetime test
Merge pull request #2592 from IgorStepanov/datetime-test-fix

[trivial] fix datetime test
improve memoize with size limit

- previous implementation was dropping complete
  hash-table whenever max size was reached

- new implementation simply replaces old values
  in a fixed size hash-table when hashes collide

- use cuckoo hashing for better space usage and to
  reduce collisions of frequently used values