Merge pull request #159 from blastehh/master

Re-added tooltips to the category buttons
Linux specific fonts, remove OSX since they have Tahoma.
Merge branch 'master' of https://github.com/adamdburton/pointshop
Added CATEGORY.ModifyTab and hook PS_CustomCategoryTab.
Added blank string checking to category description tooltips in the menu.
Update README.md
Added ServerGuard rank support.
Merge pull request #176 from alexgrist/patch-1

Added ServerGuard rank support.