Publish 0.7.0-alpha (#53)

This is nowhere near ready for 0.7.0, but releasing an alpha release
allows Fuchsia to vendor zerocopy and remove their in-tree copy
(zerocopy used to live in the Fuchsia tree before it migrated to
GitHub).

Closes #52

Cargo.toml

@@ -7,7 +7,7 @@
 [package]
 edition = "2018"
 name = "zerocopy"
-version = "0.6.1"
+version = "0.7.0-alpha"
 authors = ["Joshua Liebow-Feeser <[email protected]>"]
 description = "Utilities for zero-copy parsing and serialization"
 license-file = "LICENSE"