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.
Merge pull request #2771 from quickfur/issue13766

Issue 13766: Fix broken ddoc build for std/regex/package.d.