Apachelogs

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- Support Python 3.8
- `%s` now matches any sequence of exactly three digits. Previously, it
matched either '0' or any sequence of digits not beginning with '0'. Thanks
to [chosak](https://github.com/chosak) for the patch.

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- Improved the routine for assembling `request_time` from
`request_time_fields`:
- If the month is only available as a full or abbreviated name and the name
is not in English, try looking it up in the current locale
- If the year is only available in abbreviated form (the `%y` directive)
without a century (`%C`), treat years less than 69 as part of the
twenty-first century and other years as part of the twentieth
- When necessary, use the values of the `%G`, `%g`, `%u`, `%V`, `%U`, `%W`,
and `%w` time directives to derive the date
- If `%Z` equals `"GMT"`, `"UTC"`, or one of the names in `time.tzname`,
produce an aware `datetime`
- `%{%n}t` and `%{%t}t` now match any amount of any whitespace, in order to
match `strptime(3)`'s behavior
- **Breaking**: Renamed the `request_time_fields` keys for `%{%G}t` and
`%{%g}t` from `"week_year"` and `"abbrev_week_year"` to `"iso_year"` and
`"abbrev_iso_year"`, respectively
- `%{%p}t` can now match the empty string (its value in certain locales)
- `%{%Z}t` can now match the empty string

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- Support the `%{c}h` log directive
- `%f` and `%R` can now be `None`
- **Bugfix**: `%u` can now match the string `""` (two double quotes)
- Support `mod_ssl`'s `%{*}c` and `%{*}x` directives
- Support the `%{hextid}P` directive (as a hexadecimal integer)
- Support the `%L` and `%{c}L` directives
- Parameters to `%{*}p`, `%{*}P`, and `%{*}T` are now treated
case-insensitively in order to mirror Apache's behavior
- Refined some directives to better match only the values emitted by Apache:
- `%l` and `%m` no longer accept whitespace
- `%s` and `%{tid}P` now only match unsigned integers
- `%{*}C` no longer accepts semicolons or leading or trailing spaces
- `%q` no longer accepts whitespace or pound/hash signs

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- Gave `LogEntry` a `directives` attribute for looking up directive values by
the corresponding log format directives

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- Changed the capitalization of "User-agent" in the log format string constants
to "User-Agent"
- The `cookies`, `env_vars`, `headers_in`, `headers_out`, `notes`,
`trailers_in`, and `trailers_out` attributes of `LogEntry` are now all
case-insensitive `dict`s.

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Initial release