Add Rocket skeleton with a route prototype

This commit adds a single route `/v1/syntaxes` that returns a list of
supported syntaxes as well as defines a project layout. It's supposed to
be a starting point for all further work.

Author: ikalnytskyi

.github/workflows/tests.yml

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+name: Tests
+
+on:
+  - pull_request
+  - push
+
+env:
+  CARGO_TERM_COLOR: always
+  RUSTFLAGS: -Dwarnings
+  RUST_BACKTRACE: 1
+
+jobs:
+  cargo-fmt:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+
+      - uses: actions-rs/toolchain@v1
+        with:
+          toolchain: stable
+          profile: minimal
+          components: rustfmt
+          override: true
+
+      - uses: actions-rs/cargo@v1
+        with:
+          command: fmt
+          args: --all -- --check
+
+  cargo-test:
+    strategy:
+      matrix:
+        os:
+          - ubuntu-latest
+          - windows-latest
+          - macos-latest
+        rust-version:
+          - nightly
+
+    runs-on: ${{ matrix.os }}
+
+    steps:
+      - uses: actions/checkout@v2
+
+      - uses: actions-rs/toolchain@v1
+        with:
+          profile: minimal
+          toolchain: ${{ matrix.rust-version }}
+          override: true
+
+      - uses: actions-rs/cargo@v1
+        with:
+          command: test
+
+  cargo-rustdoc:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v1
+
+      - uses: actions-rs/toolchain@v1
+        with:
+          toolchain: nightly
+          profile: minimal
+          override: true
+
+      - uses: actions-rs/cargo@v1
+        with:
+          command: rustdoc
+          args: -- -D intra-doc-link-resolution-failure

.gitignore

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+/target

.rustfmt.toml

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+wrap_comments = true