Update from 1.20.0 to 1.21.0.

<ChangeLog>

*) Change: procfs is mounted by default for all languages when "rootfs"

isolation is used.

*) Change: any characters valid according to RFC 7230 are now allowed in

HTTP header field names.

*) Change: HTTP header fields with underscores ("_") are now discarded

from requests by default.

*) Feature: optional multithreaded request processing for Java, Python,

Perl, and Ruby apps.

*) Feature: regular expressions in route matching patterns.

*) Feature: compatibility with Python 3.9.

*) Feature: the Python module now supports ASGI 2.0 legacy applications.

*) Feature: the "protocol" option in Python applications aids choice

between ASGI and WSGI.

*) Feature: the fastcgi_finish_request() PHP function that finalizes

request processing and continues code execution without holding onto
the client connection.

*) Feature: the "discard_unsafe_fields" HTTP option that enables

discarding request header fields with irregular (but still valid)
characters in the field name.

*) Feature: the "procfs" and "tmpfs" automount isolation options to

disable automatic mounting of eponymous filesystems.

*) Bugfix: the router process could crash when running Go applications

under high load; the bug had appeared in 1.19.0.

*) Bugfix: some language dependencies could remain mounted after using

"rootfs" isolation.

*) Bugfix: various compatibility issues in Java applications.

*) Bugfix: the Java module built with the musl C library couldn't run

applications that use "rootfs" isolation.

</ChangeLog>