improve POD, add README and some helper targets

autocreate META.yml
fix -Wpointer-sign

Random.xs:50:35: warning: passing 'unsigned char *' to parameter of type 'const char *const'
converts between pointers to integer types with different sign [-Wpointer-sign]

        XPUSHs(sv_2mortal(newSVpv(rand_bytes, num_bytes)));
0.05: autocreate README