Parse signature file lines.

        @lines - A list of lines from a signature file.

        Returns None.

def parse(self, lines):
        '''
        Parse signature file lines.

        @lines - A list of lines from a signature file.

        Returns None.
        '''
        signature = None

        for line in lines:
            # Split at the first comment delimiter (if any) and strip the
            # result
            line = line.split('#')[0].strip()
            # Ignore blank lines and lines that are nothing but comments.
            # We also don't support the '!mime' style line entries.
            if line and line[0] != '!':
                # Parse this signature line
                sigline = SignatureLine(line)
                # Level 0 means the first line of a signature entry
                if sigline.level == 0:
                    # If there is an existing signature, append it to the signature list,
                    # unless the text in its title field has been filtered by user-defined
                    # filter rules.
                    if signature and not self._filtered(signature.title):
                        self.signatures.append(signature)

                    # Create a new signature object; use the size of self.signatures to
                    # assign each signature a unique ID.
                    signature = Signature(len(self.signatures), sigline)
                # Else, just append this line to the existing signature
                elif signature:
                    # signature.append(sigline)
                    signature.lines.append(sigline)
                # If this is not the first line of a signature entry and there is no other
                # existing signature entry, something is very wrong with the
                # signature file.
                else:
                    raise ParserException("Invalid signature line: '%s'" % line)

        # Add the final signature to the signature list
        if signature:
            if not self._filtered(signature.lines[0].format):
                self.signatures.append(signature)

        # Sort signatures by confidence (aka, length of their magic bytes),
        # largest first
        self.signatures.sort(key=lambda x: x.confidence, reverse=True)