Windows' native terminal, `conhost.exe`, lacks font fallback support.
This causes some of the characters used in `wttr.in`'s terminal output
to not be displayed at all - placeholders are supplied in their place.
This PR provides a mode that, when enabled, translates missing glyphs
to ones available on every platform without (*I believe*) making any
compromises regarding their meaning; see translation table below.
| Character | C-UCP | Replacements | R-UCPs |
| :--------------- | :----: | :------------------------------------ | :----: |
| NORTH WEST ARROW | U+2196 | BOX DRAWINGS LIGHT ARC DOWN AND LEFT | U+256E |
| NORTH EAST ARROW | U+2197 | BOX DRAWINGS LIGHT ARC DOWN AND RIGHT | U+256D |
| SOUTH EAST ARROW | U+2198 | BOX DRAWINGS LIGHT ARC UP AND RIGHT | U+2570 |
| SOUTH WEST ARROW | U+2199 | BOX DRAWINGS LIGHT ARC UP AND LEFT | U+256F |
| HIGH VOLTAGE SIGN | U+26A1 | BOX DRAWINGS LIGHT DOWN AND RIGHT + UP AND LEFT | U+250C + U+2518 |
It seems reasonable, per the documentation (under the section, "Weather Units"), that `?M` would enable metric ("metric (SI), but show wind speed in m/s") all by itself.
> By default the USCS units are used for the queries from the USA and the metric system for the rest of the world. You can override this behavior...
> ...
> `curl wttr.in/Amsterdam?M` # metric (SI), but show wind speed in m/s
In the USA, we have to pass `?m&M` (`https://wttr.in/?m&M`) to get metric and meters/second. If we just pass `?M`, we get USCS units for everything else and windspeed in meters/second.
