avocado.plugins.plugin: Change instance creation in Plugin class.

* Add optional parameters 'name' and 'enabled' to the constructor.
  You can just use the class variables name and enabled.
  Change plugin variable to noname and enabled variable to False.

* Include new attribute 'description' to include short documentation
  about the plugin. By default it uses the docstring of the class
  or fall backs to a message that there is no documentation.

* Add repr() facility.

Signed-off-by: Ruda Moura <rmoura@redhat.com>
avocado.plugins.lister: Get plugin docs with description attribute.

Signed-off-by: Ruda Moura <rmoura@redhat.com>
avocado.plugins.manager: Log when module has no plugin inside.

Log a message when loading external plugins discovers that
there is no plugin inside a module.

Plus: cosmetic formatting.

Signed-off-by: Ruda Moura <rmoura@redhat.com>
selftests: "Hello World!" external plugin, functional test.

Add new "hello world!" plugin, to perform functional tests
on external plugins.

Created class ExternalPluginsTest() to move all
functional tests regarding external plugins there.

Signed-off-by: Ruda Moura <rmoura@redhat.com>
selftest: Add unit tests for plugins.

Signed-off-by: Ruda Moura <rmoura@redhat.com>
docs.source.conf: Use capital letter to project.

Use `Avocado` to project name.

Signed-off-by: Ruda Moura <rmoura@redhat.com>
docs.Makefile: Rename arc to avocado.

Rename `arc` to `avocado`.
Plus:  change instructions for devhelp.

Signed-off-by: Ruda Moura <rmoura@redhat.com>
Merge pull request #163 from ruda/docs-devhelp

Build devhelp files for Avocado
Merge pull request #161 from ruda/refactory_plugins

Refactory plugins
avocado.core.tree: Add copyright note

Attributing copyright to Jaime Huerta-Cepas <jhcepas@gmail.com>,
author of the original tree node structure, that we drew inspiration
from and used part of the code (tree drawing).

CC: Jaime Huerta-Cepas <jhcepas@gmail.com>
Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
Merge pull request #164 from avocado-framework/core-tree-copyright-clarify

avocado.core.tree: Add copyright note