Addressing post-hoc PR feedback on #174 (#197)

* Add ECC & myself (Greg Pfeil) as authors

* Have the Rust impl correctly report “high s” sigs

There is a bug in the C++ side where the error is not set correctly on a
“high s” signature. The Rust side had mirrored this bug, but this
eliminates the bug in the Rust.

* Remove extra byte from sig before low-s check

This doesn’t seem to have any effect on the semantics, as the DER-formatted signature includes
lengths that ensure it will ignore extra bytes, but the C++ code removes the extra byte, so the Rust
should as well.

* Change some comments

Co-authored-by: Daira-Emma Hopwood <[email protected]>

* Appease `rustfmt`

* Have OP_DUP match the C++ impl more closely

* Address the second half of @daira’s #174 review

* Eliminate mutation from `Opcode` parsing

This now splits slices and returns the remaining pieces rather than
modifying the arguments.

* Remove obsolete comment

* Address PR comments

* Address additional comments on #174

---------

Co-authored-by: Daira-Emma Hopwood <[email protected]>

Cargo.toml

@@ -1,7 +1,12 @@
 [package]
 name = "zcash_script"
 version = "0.2.0"
-authors = ["Tamas Blummer <[email protected]>", "Zcash Foundation <[email protected]>"]
+authors = [
+    "Electric Coin Company <[email protected]>",
+    "Greg Pfeil <[email protected]>",
+    "Tamas Blummer <[email protected]>",
+    "Zcash Foundation <[email protected]>",
+]
 license = "Apache-2.0"
 readme = "README.md"
 build = "build.rs"