Bump zstd-safe to 7.0.0

Changes:
* `OutBuffer::dst` is no longer public.
* Added `OutBuffer::as_mut_ptr` and `OutBuffer::capacity`.
* Replaced libc with core::ffi for type aliases.

zstd-safe/Cargo.toml

@@ -2,7 +2,7 @@
 authors = ["Alexandre Bury <[email protected]>"]
 name = "zstd-safe"
 build = "build.rs"
-version = "6.0.6"
+version = "7.0.0"
 description = "Safe low-level bindings for the zstd compression library."
 keywords = ["zstd", "zstandard", "compression"]
 categories = ["api-bindings", "compression"]