:sig
s64 to_s64(String s, s64 fallback = 0)

:params
s : string to parse
fallback : value returned when `s` is empty or not a complete signed integer
return value : parsed s64, or `fallback`.

:see
>types
to_u64
to_f64
to_bool
int_val

:content
Parses a trimmed string as a base-10 signed integer.

The whole trimmed string must be consumed by the parser. Empty strings and partially parsed values such as `"-12px"` return the fallback.

:example
print(to_s64("-7"), "\n");
