Doxygen Updates

Replace links to missing text files removed in the 1.6.x series with links to the wiki.  Doxygen can handle URLs fine, don't atempt to quote them.  Also update the wiki link in the Readme to get everyone on the same page.

(issue ASTERISK-20259)
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Merged revisions 375698 from http://svn.asterisk.org/svn/asterisk/branches/1.8
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Merged revisions 375699 from http://svn.asterisk.org/svn/asterisk/branches/10


git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/11@375702 65c4cc65-6c06-0410-ace0-fbb531ad65f3