Now (assuming clippy is right) all (~100) uses of ` as ` in the code are
actually doing casts that could potentially silently lose data. Woooo?
At least this means that new `as`s can be extra-scrutinized, and we should
probably be adding debug_assert!s for the casts in real code.
also, previously `Numeric::Nanosecond` had a special left-aligned
parsing behavior. this commit replaces that with a newly designated
`Fixed::Nanosecond` which also handles an empty string which is
possible with an integral number of seconds.
this new module encompasses John Nagle's original RFC 2822 and 3337
parsers, updated to fully compatible to the actual standard.
the contributed `parse` module has been merged into it.
also changes the behavior of `Numeric::Nanosecond` (`%f`) to
the left-aligned digits and allows for the wider range of time zone
offsets from -99:59 to +99:59.