Merge #309: re-export ghost_cell at the root

bb970ca re-export ghost_cell at the root (Andrew Poelstra)

Pull request description:

  We use the GhostToken type in our public API (in Context::new). We should re-export the crate so users can access this type without needing to add their own dependency (and keep it in sync etc)


ACKs for top commit:
  canndrew:
    ACK bb970ca


Tree-SHA512: 27e0d4e7e7a72d00062cef67375116ab767617f62fb696b6c94b2ba000433683fed3de6e20ad316b8206444c77a37a4d472e95af88d4f965f6ddaa71af702b23

Author: apoelstra

src/lib.rs

@@ -22,6 +22,8 @@ pub extern crate serde;
 pub use bitcoin::base64;
 /// Re-export of byteorder crate
 pub extern crate byteorder;
+/// Re-export of ghost_cell crate
+pub extern crate ghost_cell;
 /// Re-export of hashes crate
 pub extern crate hashes;
 /// Re-export of hex crate