Fiat-generated code is now continuously tested

The first bits of fiat-generated code have landed into the Zig
standard library.

The code is now continuously tested on all supported platforms.

Author: jedisct1

README.md

@@ -192,7 +192,7 @@ Go | :white_check_mark: @mdempsky | :heavy_check_mark: | |
 Java | :x: Unmaintained | :heavy_check_mark: | :x: Known Buggy [#707](https://github.com/mit-plv/fiat-crypto/issues/707#issuecomment-763098543) | 
 JSON | Experimental | :white_check_mark: (only syntax) | | 
 Rust | :white_check_mark: | :heavy_check_mark: | :heavy_check_mark: ([Dalek Cryptography test-suite](https://github.com/dalek-cryptography/curve25519-dalek)) | 
-Zig | :white_check_mark: @jedisct1 | :heavy_check_mark: | | 
+Zig | :white_check_mark: @jedisct1 | :heavy_check_mark: | :heavy_check_mark: (Zig standard library) |
 
 ### Contributing a new backend