a bug fix that preventing the new sushi preview window from losing window focus
<.gitignore> ignore .xpi/.zoteroplugin files for version management
add shell script to perform auto-pack for .xpi plugin, compatible with Zotero 6.0
modify installing section and the part description of non-Windows system
1) installation note for zotero 6.0
2) add path check for quicklook application
3) Gnome Suhi installation guide
<.rdf> update zotero6.0 version support and update plugin version numbers to 1.4.3
list Bugs/Low-priority bugs/Ideas
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Close #44, #43
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