Make const, immutable, inout, and shared illegal as function attributes on the left-hand side of a function

[Martin Nowak via Digitalmars-d]

https://github.com/D-Programming-Language/dmd/pull/4043#issuecomment-58748353

There has been a broad support for this on the newsgroup discussion 
because this regularly confuses beginners.
There are also some arguments against it (particularly by Walter) saying 
that this change will put too much work on D code owners.

Let's continue with the following steps.
- add RHS/LHS function qualifiers to D's style guide
- change all code formatting (like dmd's headergen and ddoc to use RHS 
qualifiers)
- help Brian to get dfix up and running 
(https://github.com/Hackerpilot/dfix/issues/1)

Then we might revisit the topic in 6 month and see whether we have 
better arguments now.