Add Rust kernel (#163)

This adds the Rust kernel

A few notes: 

There is yet no cargo_id. (IDK if we need one.)

Second, the kernel is licensed under MIT and Apache. 
Dont know, if the syntax allows for naming both, I went with MIT. 

Third, the repo contains more than just the kernel. 
Stars might be considered unfair, this way. 
Your decision.

projects.yaml

@@ -286,6 +286,10 @@ projects:
     github_id: catherinedevlin/ipython-sql
     conda_id: conda-forge/ipython-sql
     category: magic
+  - name: Evcxr
+    github_id: evcxr/evcxr
+    category: kernels
+    license: MIT
   - name: Metakernel
     pypi_id: metakernel
     github_id: Calysto/metakernel