Move memofs and rojo-insta-ext into crates folder

crates/memofs/README.md

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+# memofs
+[![Crates.io](https://img.shields.io/crates/v/memofs.svg)](https://crates.io/crates/memofs)
+
+Implementation of a virtual filesystem with a configurable backend and file
+watching.
+
+memofs is currently an unstable minimum viable library. Its primary consumer is
+[Rojo](https://github.com/rojo-rbx/rojo), a build system for Roblox.
+
+### Current Features
+* API similar to `std::fs`
+* Configurable backends
+    * `StdBackend`, which uses `std::fs` and the `notify` crate
+    * `NoopBackend`, which always throws errors
+    * `InMemoryFs`, a simple in-memory filesystem useful for testing
+
+### Future Features
+* Hash-based hierarchical memoization keys (hence the name)
+* Configurable caching (write-through, write-around, write-back)
+
+## License
+memofs is available under the terms of the MIT license. See [LICENSE.txt](LICENSE.txt) or <https://opensource.org/licenses/MIT> for more details.