Suppress pylint warnings in tools/genast.py

These were getting annoying. I've disabled these warnings:

* missing-function-docstring
* missing-class-docstring
* missing-module-docstring
* line-too-long

and also squashed an explicit `open()` encoding warning.

Signed-off-by: Alek Ratzloff <alekratz@gmail.com>

tools/genast.py

@@ -1,4 +1,5 @@
 #!/usr/bin/env python3
+# pylint: disable=missing-function-docstring,missing-class-docstring,missing-module-docstring,line-too-long
 import abc
 import sys
 import time
@@ -283,7 +284,7 @@ def main():
     for g in GENERATE:
         sb.line(g.generate())
 
-    with open(path, "w") as fp:
+    with open(path, "w", encoding="utf-8") as fp:
         fp.write(str(sb).strip())