ported rust_base58 to no_std for sgx

[brenzi]

ported base58 library

probably not yet complete. When I try to use it, I still get

error: duplicate lang item in crate `sgx_tstd`: `f32_runtime`.
  |
  = note: first defined in crate `sgx_tstd`.

error: duplicate lang item in crate `sgx_tstd`: `f64_runtime`.
  |
  = note: first defined in crate `sgx_tstd`.

error: duplicate lang item in crate `sgx_tstd`: `panic_impl`.
  |
  = note: first defined in crate `sgx_tstd`.

error: duplicate lang item in crate `sgx_trts`: `oom`.
  |
  = note: first defined in crate `sgx_trts`.

error: aborting due to 4 previous errors

error: Could not compile `rust-base58`.

but I don't see what's pulled in

[dingelish]

Thanks! I ported a working one in 477219f. You can check the difference :-)