Added the power method for rational numbers
Added the power method for rational numbers

rust-num/num-traits,ollie27/rust_num,achanda/num,jbcrail/num,rust-num/num,rust-num/num-bigint,DonSheddow/num,rust-num/num-bigint,koverstreet/num,rust-lang/num,huonw/num,anchovieshat/num,rust-num/num-traits,jbcrail/num,jdm/num,anchovieshat/num,rust-lang/num,DonSheddow/num,Gustorn/num,koverstreet/num,rust-num/num-integer,vks/num,achanda/num,bluss/num,rust-num/num-integer,hauleth/num,Emerentius/num,Ticki/num,vks/num,rust-num/num