all missing style fields.
Set named styles to usually leave the background style empty. This
currently allows C-like filetypes to have a common default
background color.
Allow hard-coded colors to use -1 for the default color.
Add some highlighting style examples to the manual.



git-svn-id: https://geany.svn.sourceforge.net/svnroot/geany/trunk@3890 ea778897-0a13-0410-b9d1-a72fbfd435f5