Set up basic publishing workflow

Revamps the GitHub Actions workflows to the following:

**build.yml**
Verifies pull requests and commits to main.
Archives debug/release builds for them respectively.

**publish.yml**
On tag, downloads the relevant release build and publishes it as a GitHub Release.

Fixes #18

.github/workflows/build.yml

@@ -0,0 +1,61 @@
+name: Build
+
+on:
+  push:
+    branches: [ main ]
+  pull_request:
+    branches: [ main ]
+  workflow_dispatch:
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    strategy:
+      matrix:
+        platform: [ linux, windows, mac ]
+
+    steps:
+      - uses: actions/checkout@v2
+        with:
+          fetch-depth: 0
+          lfs: true
+
+      - name: Run GUT tests
+        uses: josephbmanley/[email protected]
+
+      - name: Decide debugMode
+        uses: haya14busa/action-cond@v1
+        id: debugMode
+        with:
+          cond: ${{ github.event_name == 'pull_request' }}
+          if_true: "true"
+          if_false: "false"
+
+      - name: Build game client
+        id: build
+        uses: josephbmanley/[email protected]
+        with:
+          name: NeoMori
+          preset: ${{ matrix.platform }}
+          debugMode: ${{ steps.debugMode.outputs.value }}
+
+      - name: Upload build
+        uses: actions/upload-artifact@v2
+        with:
+          name: ${{ matrix.platform }}
+          path: ${{ github.workspace }}/build/*
+
+      - name: Git describe
+        run: echo "GIT_DESCRIBE=$(git describe)" >> $GITHUB_ENV
+
+      - name: Create override.cfg
+        if: ${{ env.GIT_DESCRIBE != '' }}
+        run: echo "global/version = $GIT_DESCRIBE" > override.cfg
+
+      - name: Upload override.cfg
+        if: ${{ env.GIT_DESCRIBE != '' }}
+        uses: actions/upload-artifact@v2
+        with:
+          name: ${{ matrix.platform }}
+          path: ${{ github.workspace }}/override.cfg

.github/workflows/publish.yml

@@ -0,0 +1,35 @@
+name: Publish
+
+on:
+  push:
+    tags:
+      - '*'
+
+jobs:
+  publish:
+    runs-on: ubuntu-latest
+
+    strategy:
+      matrix:
+        platform: [ linux, windows, mac ]
+
+    steps:
+    - name: Download client
+      uses: dawidd6/action-download-artifact@v2
+      with:
+        workflow: build.yml
+        workflow_conclusion: success
+        commit: ${{ github.sha }}
+        event: push
+        name: ${{ matrix.platform }}
+        path: NeoMori
+
+    - name: Zip client
+      run: zip -q -r ${{ matrix.platform }}.zip NeoMori
+
+    - name: Publish clients
+      uses: softprops/action-gh-release@v1
+      with:
+        files: ${{ matrix.platform }}.zip
+      env:
+        GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}