Add extern templates for format_float
Add extern templates for format_float

Fixes #413.

lightslife/cppformat,mojoBrendan/fmt,alabuzhev/fmt,mojoBrendan/fmt,cppformat/cppformat,cppformat/cppformat,alabuzhev/fmt,mojoBrendan/fmt,alabuzhev/fmt,lightslife/cppformat,lightslife/cppformat,cppformat/cppformat