Adjust complilation to reduce release binary size

I'm still having cargo optimize for speed, but have configured the
following tweaks:

- Enable Link Time Optimization (LTO)
- Reduce Parallel Code Generation Units

There's no way to have cargo strip the binaries automatically, but using
the following command will handle it for you:

    $ RUSTFLAGS='-C link-arg=-s' cargo build --release

Putting these changes into place shouldn't affect the speed or behavior
of the released binary, but it does increase the compilation time. For
size reference, no optimizations resulted in a binary that was ~4.8M,and
after these steps, the binary is ~1.8M (a savings of over 60%).

See:
- https://github.com/johnthagen/min-sized-rust
- rust-lang/cargo#3483

Cargo.toml

@@ -29,3 +29,7 @@ features = ["derive"]
 
 [badges]
 maintenance = { status = "actively-developed" }
+
+[profile.release]
+codegen-units = 1
+lto = true