Add new file_line option append_on_no_match

[ripclawffb]

Currently, there doesn't exist a way to leave a file untouched if no regex matches are found.

I have a use case where I'm searching for a specific regex in multiple files and I only want to update the files that contain the regex pattern.

[tphoney]

@ripclawffb There have been a number of changes in the file_line can you see if this PR is still necessary.

More importantly apologies for the slowness to getting to this PR

[ripclawffb]

@tphoney I reviewed the changes for file_line and there still doesn't seem to be an option to not add a line if a match is not found in a file.

I also went ahead and rebased as requested.

[eputnam]

rebased again @tphoney, looks ok pending travis. @ripclawffb take a look if you'd like to make sure it still looks ok to you.

[ripclawffb]

@eputnam thanks! looks good to me.