Refactor code

Change mpc.py to auto generate antlr4 files without having to run manualy. Also add a small command line ultility.
Remove commented import in others files, and update README

tools/genANTLR4.py

@@ -0,0 +1,39 @@
+import os
+import subprocess
+
+
+ANTLR_JAR = os.environ.get('ANTLR_LIB')
+
+if ANTLR_JAR is None:
+    # fall back, not recommended
+    ANTLR_JAR = '../external/antrl4.jar'
+
+files_from_antlr4 = [
+    'parser/MP.interp',
+    'parser/MPLexer.interp',
+    'parser/MPLexer.py',
+    'parser/MPLexer.tokens',
+    'parser/MPParser.py',
+    'parser/MP.tokens',
+    'parser/MPVisitor.py'
+]
+
+
+def generate():
+    if all(list(map(os.path.isfile, files_from_antlr4))):
+        return
+    gen_antlr_class_cmd = [
+        "java",
+        "-jar",
+        ANTLR_JAR,
+        "-no-listener",
+        "-visitor",
+        "parser/MP.g4"
+    ]
+    subprocess.run(gen_antlr_class_cmd)
+
+
+def regenerate():
+    for f in files_from_antlr4:
+        os.remove(f)
+    generate()