attributes for inline asm
Make std.file.symlink safe
(trivial) (ddoc) more descriptive std.concurrency doc.

`ownerTid`/`childTid` are more descriptive/obvious when reading than just `tid` here.
Merge pull request #2594 from tom-tan/safe-file-symlink

Make std.file.symlink safe
readd std.metastrings as empty and deprecated module

- Removing the deprecated module silently broke
  and code that still imported the module without
  using any of it's functions.
Merge pull request #2595 from kiith-sa/patch-2

(trivial) (ddoc) more descriptive std.concurrency doc.
Merge pull request #2596 from MartinNowak/metastrings

readd std.metastrings as deprecated module
Merge pull request #2572 from MartinNowak/asmAttributes

attributes for inline asm