Document opDollar.
Clarify about opDollar without compile-time argument.
Fix wrong example code.
Move opDollar docs to its own section.

Expand with feedback from Kenji, Don, et al.
Add std.regex "what's new" to 2.064 changelog
Merge pull request #400 from blackwhale/regex-64

Add std.regex "what's new" to 2.064 changelog
Add changelog for the additional new features in 2.064
Merge pull request #401 from 9rnsr/2064_changelog

Add changelog for the additional new features in 2.064
Update LDC download links to 0.12.0.

Also rearranges the links to be in the same order as for DMD.
Fix 3 changelog typos
Merge pull request #403 from ntrel/changelog-2.064-fixes

Fix 3 changelog typos
Replace link with FULL_XREF so PDF build can work.
Merge pull request #292 from quickfur/opdollar

Document opDollar (issue 7520)
fix Issue 9665 - Structure constant members can not be initialized if have opAssign

Describe about field initialization behavior.
Merge pull request #402 from klickverbot/ldc-0.12.0

Update LDC download links to 0.12.0.
Fix wrong code in unittest example.
Merge pull request #407 from AndrejMitrovic/FixupUnittest

Fix wrong code in unittest example.
Merge pull request #404 from 9rnsr/fix9665

Issue 9665 - Structure constant members can not be initialized if have opAssign
$ replaces "length" as the length of a tuple defined within [ ]s.
Merge pull request #408 from rjmcguire/master

$ replaces "length" as the length of a tuple defined within [ ]s.