[phobos] Deprecation of std.regexp

[Jonathan M Davis]

It looks like std.regexp was marked in its documentation as deprecated in 
2.053. It was not actually deprecated (the deprecation modifier is missing), 
but if it has indeed been deprecated (and std.regex has been around for a 
while, so it's not exactly a surprise), then it needs to actually be 
deprecated, and the rest of Phobos needs to be using std.regex instead. I can 
easily deprecate the function (after all, all you have to do is add 
deprecated: near the top of the file), but since I've never used either of the 
regex modules, I'm ill-suited to convert the rest of Phobos to use std.regex. 
So, I'd appreciate it if someone who is actually familiar with the two modules 
would convert the rest of Phobos to use std.regex sometime prior to the next 
release, and then we can actually deprecate std.regexp. Worse comes to worst, 
I can take a crack at it, but it would be much faster if someone who's 
familiar with the regex modules did it.

Now, we may actually want to change std.regexp to "scheduled for deprecation" 
rather than deprecated simply because there are other functions in Phobos 
which take stuff from std.regexp but not std.regex (such as the version of 
std.file.listdir which takes a RegExp) have not yet been scheduled for 
deprecation, let alone deprecated, but regardless, we need to change the rest 
of Phobos to use std.regex or we won't be able to actually deprecate and 
remove std.regexp (well, I suppose that we _could_ deprecate it as-is, but it 
seems to me to be a bad idea to deprecate something when Phobos is still using 
it in its API elsewhere).

- Jonathan M Davis