chore(ci): add github ci script

This commit introduces a script that will enforce the following
constraints:

- Tests are successful
- Rustfmt is executed for every Rust source
- Clippy warnings are resolved

The same model of Miden VM is adopted here. However, `no-std` check
wasn't added because the library, as of the moment, doesn't implement
that.

closes #3

.github/pull_request_template.md

@@ -0,0 +1,9 @@
+## Describe your changes
+
+
+## Checklist before requesting a review
+- Repo forked and branch created from `next` according to naming convention.
+- Commit messages and codestyle follow [conventions](./CONTRIBUTING.md).
+- Relevant issues are linked in the PR description.
+- Tests added for new functionality.
+- Documentation/comments updated according to changes.

.github/workflows/ci.yml

@@ -0,0 +1,66 @@
+name: CI
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+    types: [opened, repoened, synchronize]
+
+jobs:
+  test:
+    name: Test Rust ${{matrix.toolchain}} on ${{matrix.os}}
+    runs-on: ${{matrix.os}}-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        toolchain: [stable, nightly]
+        os: [ubuntu]
+    steps:
+      - uses: actions/checkout@main
+      - name: Install rust
+        uses: actions-rs/toolchain@v1
+        with:
+          toolchain: ${{matrix.toolchain}}
+          override: true
+      - name: Test
+        uses: actions-rs/cargo@v1
+        with:
+          command: test
+
+  clippy:
+    name: Clippy
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@main
+      - name: Install minimal stable with clippy
+        uses: actions-rs/toolchain@v1
+        with:
+          profile: minimal
+          toolchain: stable
+          components: clippy
+          override: true
+
+      - name: Clippy
+        uses: actions-rs/cargo@v1
+        with:
+          command: clippy
+          args: --all -- -D clippy::all -D warnings
+
+  rustfmt:
+    name: rustfmt
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@main
+      - name: Install minimal stable with rustfmt
+        uses: actions-rs/toolchain@v1
+        with:
+          profile: minimal
+          toolchain: stable
+          components: rustfmt
+          override: true
+
+      - name: rustfmt
+        uses: actions-rs/cargo@v1
+        with:
+          command: fmt
+          args: --all -- --check