todo statement, -beta and -airy compiler options

[Manfred Nowak]

It seems common practice to put a hint to not yet implemented code in 
a comment starting with "TODO" or similar wording.

Therefore I believe that compiler assistance for this behaviour 
should be available.

The language allows for a `todo' statement, which may be a keyword-
only  statement or similar to a line comment starting with keyword 
`todo'.

The compiler allows for an option "-beta", which has the semantics of 
issuing a "still alpha stage" error iff there are `todo' statements 
in the code.

The current semantics of the compiler option "-release" then sticks 
with a new 
"-airy" or
"-dmc" ( short for "devil may care")
option.

The "-release" option becomes a shortcut for
"-beta -airy -O -inline".

The current semantics of "-O" and "-inline" is changed so that an 
XORing with the semantics provided by "-release" takes place. I.e.:
- if "-release" is present on the command line
-- any additional "-O" disables optimization, and
-- any additional "-inline" disables inlining
- if "-release" is _not_ present on the command line, then the 
command line options "-O" and "-inline" keep their current semantics.

-manfred