Bump crate version to 0.8.0-dev to show that tip of main branch is go…

…ing to land in a new minor version

I'm not currently planning to cut this release just yet, but this avoids confusion of thinking
that the main branch tracks the v7 train when there's really a separate v0.7 branch for that.

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "elf"
-version = "0.7.3"
+version = "0.8.0-dev"
 authors = ["Christopher Cole <chris.cole.09@gmail.com>"]
 license = "MIT/Apache-2.0"
 repository = "https://github.com/cole14/rust-elf/"