Docs: update CL implementations' time precision

Fix a few docstrings.

Add format-rfc1123-timestring documentation

in `doc/local-time`.

Add :short-year documentation

in `src/local-time` and `doc/local-time`.

Follow-up to bbcf4e87.

Correct documentation and create test for adjust-timestamp.

Make docstring and documentation reflect actual behavior of function.

Show that, when invoked with (offset :day-of-week ...),
adjust-timestamp find the day corresponding to the specified offset
within the week of the given timestamp.

Use 'gettimeofday' on LispWorks (Darwin and GNU/Linux).

Alter timestamp/= to match behavior of cl:/=

The most important change is to have the padding character #\0.

The behavior of /= is different in that it cannot be done pair-wise, so
it needs its own implementation.

This fixes issue #72.

Fixes for Allegro

Fix loop initialization warnings on LispWorks.

Fixes the following warning:

Local Variable Initialization clause (the binding of LOCAL-TIME::PARAMS) follows iteration forms but will be evaluated before them.

Higher-resolution timestamps for CCL on Windows.

Read timezones corrrectly when repository path is a symlink

Improve project system definitions

Default to UTC on any zone problem during loading.

Fixes issue #63.

Export clone-timestamp from local-time package

This commit fixes issue #64.

Improve timestamp printing

Mention license in ASDF file, too

This makes it easier to use `asdf:system-license`.
Thanks a lot!

Use `write-char` to print the `@` before timestamp because using `princ`
uses all the printing machinery, and, most importantly, it uses sharing
detection.  So if two or more timestamps are in the same structure the
sharpsign-sharpsign syntax is used to print them.

Fix error in ISO week calculation.

Include -43200 in the type specifier of timezone-offset type

This fixes issue #52.

This fixes issue #50.

Create a new clock which adjusts for leap seconds.