tools: remove hardcoded references to paths

tools/as.py

@@ -1,12 +1,14 @@
 import argparse
 import enum
 import lark
+import os
 import struct
 import sys
 
 import obj_pb2
 
-GRAMMAR_FILE = '/home/paulmathieu/vhdl/tools/as.ebnf'
+_HERE = os.path.dirname(__file__)
+GRAMMAR_FILE = os.path.join(_HERE, 'as.ebnf')
 
 opcodes = {
         'nop'  : lambda: '0000',