More docstrings

[digikar99]

Hi!

Would there be any interest in including more docstrings from the documentation? Besides being helpful to users, this also makes things on https://github.com/cl-library-docs/common-lisp-libraries/ more scaleable. (My current plan is to keep separate files for manually written prologue-files. These files would be appended by docstrings to create the final documentation files for user consumption - so this relies much on the existence of docstrings to be of good use.)

If this is okay, I'd be willing to do this over the next month and issue a PR. Some examples where there is much documentation but no docstrings include the symbols in the section on Timezones, examples provided under preprovided format constants, as also the adjust-timestamp macros.

[digikar99]

• time vs time-of-day: the manual mentions time in the context of timestamps, but the library exports time-of-day; timezone is mentioned but not exported
• Docstringdecode-timestamp is inconsistent with the manual; manual looks consistent with the code
• also, the docstring for parse-timestring mentions an unexported split-timestring, is split-timestring intended to be exported?