Added comment describing bitcasts.go.
Added comment describing bitcasts.go.

gopherjs/gopherjs,roth1002/gopherjs,Yanjing123/gopherjs,Archs/gopherjs,albrow/gopherjs,albrow/gopherjs,Yanjing123/gopherjs,jargv/gopherjs,gopherjs/gopherjs,ebroder/gopherjs,jeremyschlatter/gopherjs,rasata/gopherjs,jargv/gopherjs,govlas/gopherjs,bpowers/gopherjs,flimzy/gopherjs,roth1002/gopherjs,roth1002/gopherjs,Archs/gopherjs,ebroder/gopherjs,flimzy/gopherjs,rasata/gopherjs,rasata/gopherjs,jeremyschlatter/gopherjs,nmfzone/gopherjs,jargv/gopherjs,govlas/gopherjs,gopherjs/gopherjs,nmfzone/gopherjs,ebroder/gopherjs,govlas/gopherjs,flimzy/gopherjs,nmfzone/gopherjs,jeremyschlatter/gopherjs,bpowers/gopherjs,Yanjing123/gopherjs,Archs/gopherjs,gopherjs/gopherjs,gopherjs/gopherjs,bpowers/gopherjs,albrow/gopherjs