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This reverts commit 7f62f7f1.
This is already covered in #5145.

 - port check fixed
 - removed 2 unused parameter warnings
 - one typo corrected

Trivial change. Commiting on my discretion.

    Fixed unused parameter errors
    Fixed doxygen errors
    Commentary changes
    Removed reference to .spec file from commentary
    TSIGKeyListParser now uses only one instance of TSIGKeyInfoParser
    src/bin/d2/d2_parser.yy -  added upper limit to port tests
    Updated unit tests to use "example.com"

 - lines wrapped to 100 columns (according to our coding guidelines)
 - explained what @3 means in bison
 - created link to wiki page about regenerating parser code
 - added terminology page that explains what CA and D2 are
 - corrected order of the files in Makefile.am