Auto merge of #149 - rust-num:i-complex-constant, r=cuviper
Auto merge of #149 - rust-num:i-complex-constant, r=cuviper

Add complex `i` constant function

None

vks/num,rust-num/num-integer,rust-num/num-traits,DonSheddow/num,jbcrail/num,rust-lang/num,rust-num/num-traits,rust-num/num-bigint,koverstreet/num,anchovieshat/num,anchovieshat/num,rust-num/num,jbcrail/num,koverstreet/num,rust-lang/num,rust-num/num-integer,rust-num/num-bigint,DonSheddow/num,vks/num,rust-num/num