[rapidxml] revision

[FabioLolix]

Hello, I have come across rapidxml as a dependency of other pkgbuilds, I build them all in clean chroot, rapidxml initially failed because of missing git as makedepends so I take a look

• pkgname don't have to be in pkgdesc
• please use upstream url
• please use upstream source archive
• removed not needed provides=("rapidxml")
• use sha256 or higher for cheksum
• some style changes, if you don't like let me know