Add doc of @filename in intro_patterns.rst

I noticed that the @filename notation for the --limit argument was not
conveniently described.

This patch adds a simple example to the intro_patterns.rst file.
Fix several it's/its errors in the documentation.
Creating initial framework for refactoring core codebase
Signatures
Some signature related things, prior to starting test scaffolding
Some restructuring.
Have a parallel development and test tree.
Make target for nosetests, no need to set library path for previous tests
Fix target in makefile
Move v2 out of the package tree so it does not yet appear.
Remove typo and intermediate dir.
Plan for unified CLI with subcommands?
Add readlink filter doc

As requested at request pull #9213, I'm proposing updathing this doc. Do you have man pages where I can update this too ?

Thanks
Add one line example for looking up through etcd
Make dynamic inventory return byte str, not unicode
Initial work to refactor Task
Merge pull request #9252 from kim0/patch-1

Add one line example for looking up through etcd
Merge pull request #9250 from i5513/patch-2

Add readlink filter doc
Merge pull request #9239 from direvus/grammar-its

Fix several it's/its errors in the documentation.
Merge pull request #9237 from jkleckner/add-limit-from-file-doc

Add doc of @filename in intro_patterns.rst