Fix broken ddoc build for std/regex/package.d.
Update std.range.* docs.

The previous docs were simply dissected from the original std.range docs, and
the text in each module is truncated and awkward to read. The main package.d
docs were also missing links to the submodules. So, update the docs to reflect
the current state of things.
Fix broken PHOBOSSRC link.

This is caused by Ddoc's "helpful" auto-highlighting of every occurrence of the
name of the module, including places where it's not very helpful.
allow casting Typedef to another Typedef
fix issue 11434
added version(Posix) to unittest
Add PreserveAttributes flag to copy function to preserve file attributes (issue 11434) and current behavior (not at the same time)

Avoid compiler errors from new versions

rename flag

add documentation and spaces
Merge pull request #2776 from IgorStepanov/Typedef-opCast

allow casting Typedef to another Typedef
Merge pull request #2771 from quickfur/issue13766

Issue 13766: Fix broken ddoc build for std/regex/package.d.
Merge pull request #2784 from kuettler/issue_11434

Issue 11434: std.file.copy doesn't preserve file attributes (eg: executable mode etc)
fix comment
Merge pull request #2789 from kuettler/issue_11434

Issue 11434: std.file.copy doesn't preserve file attributes (eg: executable mode etc) -- comment fix
Avoid unnecessary enforce
Fix Issue 12114
buildNormalizedPath shouldn't normalize current path to empty string
Added unittests (not tested on windows platform)
Doc update
Merge pull request #2790 from sinkuu/remove

Avoid unnecessary enforce
Issue 13837 - Allow names for tuple
Add BitFlags template

BitFlags is a typecons template for storing OR combinaton of enum
values in a type safe fashion.
code style (braces) and !is comparison