std.unittests [updated] for review

[Jens Mueller]

Masahiro Nakagawa wrote:
> 
> I vote Andrei's suggestion, std.exception is better than new std.unittests.
> I think testing module should provide more features(e.g. Mock, Stub...).
> Your helpers help assert writing style but not help testing.
> In addition, std.exception already defined similar functions.

I do not like putting it in std.exception. Maybe the name std.unittest
is also not good. I would propose std.assert if assert wasn't a keyword.
When I use std.exception I want to handle situations that are part of
the spec (i.e. exceptions) whereas Jonathan's module helps me writing
asserts (that's most of the time unittests).
Basically it helps me verifying behavior according to a spec. I want to
keep the dichotomy of errors and exceptions. Putting both things in one
module is rather strange to me. What are the arguments for putting it in
std.exception? I find the size a rather weak argument. I thought about
providing an assertDeath ones std.process is redone.
And even though enforce and assert are mirroring each other they are
used in different contexts. I would _not_ expect helpers for writing
assertions (Assert_Error_) in a module named std.exception.

Jens