Rename *Tuple symbols

[WalterBright]

Does the following renames in std.traits:

isExpressionTuple => isExpressions
ParameterTypeTuple => Parameters
FieldTypeTuple => Fields
ParameterDefaultValueTuple => ParameterDefaults

and in std.typetuple:

TypeTuple => Arguments

The original names are kept and documented as aliases kept for legacy compatibility. I didn't do a global search/replace in Phobos to change the names, preferring to keep this PR simple. Over time, as various modules get worked on, the names can be changed.

[MartinNowak]

Gets rid of TypeTuple except for in the module name.

[MartinNowak]

Auto-merge toggled on

[andralex]

Next step is to add a new module name and have the old one just use it?

[MartinNowak]

Next step is to add a new module name and have the old one just use it?

#3265

[dnadlinger]

wat.

[MartinNowak]

This gets rid of TypeTuple which was deemed confusing because it's not really a tuple and can contain more than types.

[s-ludwig]

Ehem, this doesn't get rid of TypeTuple, but gets rid of "TypeTuple" as part of template names where it made perfect sense. std.traits.Fields has a totally misleading name now, while FieldTypeTuple was perfectly fine. Name it FieldTypes if you want, but just Fields? There are also still other names, such as FieldNameTuple. Why hasn't that been renamed to Fields? Or FieldNames?

Also, this change isn't really documented well in the change log. It just says "changed FieldTypeTuple".

I think this should either be reverted, or all *Tuple symbols should just drop the Tuple part, but not the Type/Name part. Like it is now, it just adds inconsistency and confusion (I first tried to do typeof(Fields!T) and had to double-check that it already returns types).