Add Kix's name to the authors list

If one looks at crates.io or the git index it looks like I wrote this
crate but that is wholeheartedly untrue, Kix wrote almost all the code
in this crate IIRC. I just pulled it all out of `rust-bitcoin`.

Put Kixunil's name at the front of the author's list. Leave Andrew's
there in second place because he is the crate owner, and reviewed
everything. Omit my name because I have only chopped and changed trivial
things and am only likely to polish things going forwards.

Cargo.toml

@@ -1,7 +1,7 @@
 [package]
 name = "hex-conservative"
 version = "0.1.1"
-authors = ["Andrew Poelstra <[email protected]>"]
+authors = ["Martin Habovštiak <[email protected]>", "Andrew Poelstra <[email protected]>"]
 license = "CC0-1.0"
 repository = "https://github.com/rust-bitcoin/hex-conservative"
 documentation = "https://docs.rs/hex-conservative/"