Document Error and its constructor
Add ENOTSUP for linux, which maps to EOPNOTSUPP

glibc aliases ENOTSUP to EOPNOTSUPP. We therefore should declare it as well
as EOPNOTSUPP.
demangle @nogc
Mark first param of apply functions as 'in'
Add unittests from _aApplyR.d
Merge pull request #769 from dsp/linux/ENOTSUP

Add ENOTSUP for linux, which maps to EOPNOTSUPP
Merge pull request #771 from ibuclaw/inparm

Mark first param of apply functions as 'in'
Merge pull request #770 from WalterBright/demangle_nogc

demangle @nogc
Merge pull request #765 from ntrel/doc-Error

Document Error and its constructor