std.json: ensure objects contain keys
Merge pull request #2186 from Yoplitein/master

std.json: throw exception if a key does not exist
Avoid double lookup in opIndex for std.json.
Merge pull request #2197 from AndrejMitrovic/Fixup2186

Avoid double lookup in opIndex for std.json.
Merge pull request #2199 from yebblies/valisttype

Do not make assumptions about the type of va_list (win64 edition)