move format to std.format

The reason is to do not import `std.uni` tables, `std.string` and
probably `std.algorithm`. Note that format is used in CTFE code and
`Exception` handing.

 And it is more comfortable to import `format` from `std.format`.
std.format: clean imports (2)
update scope imports in std.conv
remove import std.math : pow from std.uni
update scope imports in std.algorithm
update scope imports in std.exception
doFormat -> template
update scope imports in std.typecons
update scope imports in std.functional
update scope imports in std.range
move sformat to format