Add some comments to tutils.h.
Add some comments to tutils.h.

dlz1123/taglib,videolabs/taglib,davispuh/taglib,videolabs/taglib,taglib/taglib,Distrotech/taglib,i80and/taglib,taglib/taglib,i80and/taglib,dlz1123/taglib,davispuh/taglib,black78/taglib,videolabs/taglib,pbhd/taglib,davispuh/taglib,pbhd/taglib,pbhd/taglib,black78/taglib,black78/taglib,dlz1123/taglib,taglib/taglib,MaxLeb/taglib,TsudaKageyu/taglib,TsudaKageyu/taglib,MaxLeb/taglib,Distrotech/taglib,Distrotech/taglib,TsudaKageyu/taglib,MaxLeb/taglib,i80and/taglib