Cut down WANT_FROM_OTHER_CRATES

rust itself:

 * specialization for u8.

 * generic arrays via associated consts or whatever it's called.

 * when an enum is c-like, implement try_into for numbers.  (but see num_enum and many similar crates.)

 * specialization.

 * existential types.

curve25519-dalek:

* let me go from a montogmery point to a compressed edwards point.

*-dalek:

* let me use the right rand trait kthx

dalek-crypto:

* Upgrade to latest version of rand crate.

ed25519-dalek:

* defer signature verification without prehash mode.  A signature

  future would be great.

base64:

* multiline support.

* defer signature verification without prehash mode.

phf:

* much cheaper hash function

* get raw signed data, to allow multiple signed formats.

crypto:

* key agreement trait

* key agreement trait (Or do they have one already?)

ed25519 trait:

* batch support.

* batch support. (or do they have one already?)

native-tls:

* Support for RFC5705 exporters

* Support for RFC5705 exporters where available.