DMD 0.163 release

[Walter Bright]

James Dunne wrote:
> What's so bad about context dependent keywords?

Then the lexer cannot tokenize the source without doing a parse. This 
negatively impacts tools that need to do so like Ddoc.

Furthermore, it is confusing if one also has a typedef named 'as'. 
Having keywords be distinct, and always distinct, from identifiers means 
you can look at code and see what's an identifier and what's a keyword 
without confusion.