Rationalize README file handling:
1.) Install only README files that are relevant to the Postfix binaries
distributed with NetBSD.
2.) Create a single list of the above files that is used for bot

Rationalize README file handling:
1.) Install only README files that are relevant to the Postfix binaries
distributed with NetBSD.
2.) Create a single list of the above files that is used for both the
text versions and HTML versions.

Problem detected by wizd(8).

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Add one more file back.

More corrections.

Don't install installation documentation. It is highly irrelevant.

Don't install files related to other operating systems.

Update list of HTML pages.

Install documentation and manual pages for Postfix's memcache client support.

Build new Postfix components dnsblog(8), postscreen(8) and tlsproxy(8)
and install new documentation files.

Mirror the file system structure of the installed files in the structure
of the Makefiles as suggested by Christos Zoulas.