Fix link to Rust style guide (#502)

* Fix link to Rust style guide

* Link to SUMMARY.md

* Update STYLE.md

The style guide appears to be "officially" published here: https://doc.rust-lang.org/style-guide/index.html

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Co-authored-by: Justin W Smith <[email protected]>

STYLE.md

@@ -1,3 +1,3 @@
 # Style Guide for *aws-lc-rs*
 
-This project follows the standard Rust Style Guidelines [documented here](https://github.com/rust-lang/fmt-rfcs/blob/master/guide/guide.md).
+This project follows the standard Rust Style Guidelines [documented here](https://doc.rust-lang.org/style-guide/index.html).