configure.ac: bump API version to 0.5.1
configure.ac: bump API version to 0.5.1

bump api for vp8 svct decoder

stripes416/libyami,01org/libyami,YuJiankang/libyami,lizhong1008/libyami,YuJiankang/libyami,lizhong1008/libyami,lizhong1008/libyami,01org/libyami,01org/libyami,stripes416/libyami,YuJiankang/libyami,stripes416/libyami