Fab automation (#2)

- Use KiKit for fab automation
- Add splitflap scripts for exporting pcb pdfs, and switch to splitflap script for 3d rendering (for consistency with fab automation)
- Added support in 3d rendering scripts for soldermask & silkscreen colors, option to skip virtual components
- Added silkscreen to base and screen pcbs for commit and date info

util/rev_info.py

@@ -0,0 +1,32 @@
+import datetime
+import subprocess
+
+def git_short_rev():
+    try:
+        return subprocess.check_output([
+            'git',
+            'rev-parse',
+            '--short',
+            'HEAD',
+        ]).decode('utf-8').strip()
+    except Exception:
+        raise RuntimeError("Could not read git revision. Make sure you have git installed and you're working with a git clone of the repository.")
+
+def current_date():
+    return datetime.date.today().strftime('%Y-%m-%d')
+
+def git_date(short=True):
+    try:
+        iso = subprocess.check_output([
+            'git',
+            'log',
+            '-1',
+            '--format=%ci',
+            'HEAD',
+        ]).decode('utf-8').strip()
+        if short:
+            return iso.split(' ')[0]
+        else:
+            return iso
+    except Exception:
+        raise RuntimeError("Could not read git commit date. Make sure you have git installed and you're working with a git clone of the repository.")