[dmd-internals] DMD pull requests - Ddoc documentation

[Walter Bright via dmd-internals]

A rather large percentage of PRs for DMD get submitted with malformed Ddoc 
function comments or completely missing function comments.

Because the Ddoc documentation for it is online:

     http://dlang.org/phobos/ddmd_expression.html

DMD must be an example of how to do it right.

By malformed I mean not following the Ddoc conventions of having `Params:` and 
`Returns:` sections where appropriate.

For those with merge privileges, please do not merge such PRs.

Please exercise good judgement. For example, override functions that do not 
change the interface do not need to copy the introducing function's documentation.