doc_main.txt: Set alphabetical order within list and deleted linebreaks, that...

doc_main.txt: Set alphabetical order within list and deleted linebreaks, that are not needed as I noticed.
header.html: change to UTF-8 charset, search hits were not shown correct before.

git-svn-id: https://smartmontools.svn.sourceforge.net/svnroot/smartmontools/trunk@2954 4ea69e1a-61f1-4043-bf83-b5c94c648137