Install plugin from CLI (#304)

* add install command

* cargo fmt

* filter spec files

* Update src/cli/plugin.rs

Co-Authored-By: Lucien Greathouse <me@lpghatguy.com>

* Update src/cli/plugin.rs

Co-Authored-By: Lucien Greathouse <me@lpghatguy.com>

* fix comments

* encode plugin with rbx_binary

* update build script

* refactor pathbuf error into io error

* fix rojo typo

* remove snafu

* Update `snapshot_from_fs_path`

* Print `rerun-if-changed` even for directories, in order to run the
  build.rs script when files are added.

* Switch `filter_map` loop to a regular for loop. I like the FP-style
  iterator stuff in Rust, but I think Result handling is easier in a
  normal loop. Also, I don't believe the result of read_dir implements
  `ExactSizedIterator`, so some of the wins of map+collect aren't there.

* Replace Result::unwrap with ? in build.rs

* Simplify error handling code in runtime

* Checkout with submodules

Co-authored-by: Lucien Greathouse <me@lpghatguy.com>

.github/workflows/ci.yml

@@ -16,6 +16,8 @@ jobs:
 
     steps:
     - uses: actions/checkout@v1
+      with:
+        submodules: true
 
     - name: Setup Rust toolchain
       run: rustup default ${{ matrix.rust_version }}