all: AVX-512 (#217)

Extends avo to support most AVX-512 instruction sets.

The instruction type is extended to support suffixes. The K family of opmask
registers is added to the register package, and the operand package is updated
to support the new operand types. Move instruction deduction in `Load` and
`Store` is extended to support KMOV* and VMOV* forms.

Internal code generation packages were overhauled. Instruction database loading
required various messy changes to account for the additional complexities of the
AVX-512 instruction sets. The internal/api package was added to introduce a
separation between instruction forms in the database, and the functions avo
provides to create them. This was required since with instruction suffixes there
is no longer a one-to-one mapping between instruction constructors and opcodes.

AVX-512 bloated generated source code size substantially, initially increasing
compilation and CI test times to an unacceptable level. Two changes were made to
address this:

1.  Instruction constructors in the `x86` package moved to an optab-based
    approach. This compiles substantially faster than the verbose code
    generation we had before.

2.  The most verbose code-generated tests are moved under build tags and
    limited to a stress test mode. Stress test builds are run on
    schedule but not in regular CI.

An example of AVX-512 accelerated 16-lane MD5 is provided to demonstrate and
test the new functionality.

Updates #20 #163 #229

Co-authored-by: Vaughn Iverson <vsivsi@yahoo.com>

.github/workflows/stress.yml

@@ -0,0 +1,50 @@
+name: stress
+
+permissions:
+  contents: read
+
+on:
+  schedule:
+    - cron: '33 3 * * 6'
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    env:
+        GOFLAGS: -tags=stress
+    steps:
+    - name: Install Go
+      uses: actions/setup-go@37335c7bb261b353407cff977110895fa0b4f7d8 # v2.1.3
+      with:
+        go-version: 1.17.x
+    - name: Configure Go Environment
+      run: |
+        echo GOPATH=${{ runner.workspace }} >> $GITHUB_ENV
+        echo ${{ runner.workspace }}/bin >> $GITHUB_PATH
+    - name: Go Environment
+      run: go env
+    - name: Checkout code
+      uses: actions/checkout@5a4ac9002d0be2fb38bd78e4b4dbde5606d7042f # v2.3.4
+      with:
+        persist-credentials: false
+    - name: Bootstrap
+      run: ./script/bootstrap
+
+    - name: Generate
+      run: ./script/generate
+    - name: Status
+      run: git status
+
+    - name: Build
+      run: go build ./...
+    - name: Test
+      run: go test -bench . ./...
+    - name: Coverage
+      run: ./script/coverage
+
+    - name: Upload Stress Unit Test Coverage
+      uses: codecov/codecov-action@51d810878be5422784e86451c0e7c14e5860ec47 # v2.0.2
+      with:
+        token: ${{ secrets.CODECOV_TOKEN }}
+        files: unittests.coverprofile
+        flags: stress