Issue 7059 - Modify fldiff so it can handle multiple files

README.md

 # python-abp
 
 This repository contains a library for working with Adblock Plus filter lists
 and the script that is used for building Adblock Plus filter lists from the
 form in which they are authored into the format suitable for consumption by the
 adblocking software.
 
 ## Installation
 
 Prerequisites:
@@ skipping 74 matching lines @@
 
 You can clone the necessary repositories to a local directory and add `-i`
 options accordingly.
 
 ## Rendering diffs
 
 A diff allows a client running ad blocking software such as Adblock Plus to update
 the filter lists incrementally, instead of downloading a new copy of a full list
 during each update. This is meant to lessen the amount of resources used when updating
 filter lists (e.g. network data, memory usage, battery consumption, etc.), allowing 
 clients to update their lists more frequently using less resources.

[Vasily Kuznetsov, 2018/10/24 11:30:08]

We normally try to limit line length to <80 characters in the documentation
files. It's not really documented anywhere but it's pretty consistent and it's
easier to read such files so I would recommend to format this section this way.

 
-Python-abp contains a script that produces the diff between two versions of a
-filter list called `fldiff`:
+Python-abp contains a script called `fldiff` that will find the diff between the lastest

[Vasily Kuznetsov, 2018/10/24 11:30:08]

Nit: should it be "latest"?

+filter list, and any number of previous filter lists:
 
-    $ fldiff base.txt latest.txt output.txt
+    $ fldiff -o diffs/easylist -l last-easylist.txt archive/*
+where `-o diffs/easylist` is the (optional) directory where the diffs should be written,
+`-l last-easylist.txt` is the most recent version of the filter list, and
+`archive/*` is the directory where all the the archived filter lists are. When called
+like this, the shell should automatically expand the `archive/*` directory, giving the script
+each of the files separately.
 
-This will produce a diff that shows how a client may get from `base.txt` to
-`latest.txt`, and write the output to `output.txt`. The output argument is
-optional. If ommitted, the data will be written to `stdout`.
+The output of each `list[version].txt` will be written to `diffs/diff[version].txt`.
+The output argument is optional. If ommitted, the data will be written to `stdout`.
 
 The script produces three types of lines, as specified in the [technical specification][5]:
 * Special comments of the form `! <name>:[ <value>]`
 * Added filters of the form `+ <filter-text>`
 * Removed filter of the form `- <filter-text>`
 
 ## Library API
 
 Python-abp can also be used as a library for parsing filter lists. For example
 to read a filter list (we use Python 3 syntax here but the API is the same):
@@ skipping 83 matching lines @@
 
 Now you can use the functions with `abp$functionname`, e.g. 
 `abp.line2dict("@@||g.doubleclick.net/pagead/$subdocument,domain=hon30.org")`
 
 
  [1]: https://adblockplus.org/filters#special-comments
  [2]: http://pytest.org/
  [3]: https://tox.readthedocs.org/
  [4]: https://github.com/numpy/numpy/blob/master/doc/HOWTO_DOCUMENT.rst.txt
  [5]: https://docs.google.com/document/d/1SoEqaOBZRCfkh1s5Kds5A5RwUC_nqbYYlGH72sbsSgQ/