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.
- Format string is internally represented as a series of formatting
items. Items can be directly given to now-public `format::format`
function as well.
- Format string parser is separated to `format::strftime` module.
This is to allow for potentional alternative formatting syntaxes.
- `DelayedFormat` now receives an iterator for formatting items.