Version 2.0.5

This PR:

* represents the ongoing development for the next version (`2.0.5`).
* is a showcase to show what is being implemented.
* is a place to discuss and form the next version.

After arriving a stable state, I'll merge it to master and publish to Package Manager.

Here is some changes:

As #132 proposes, pressing <kbd>Enter</kbd> in a blockquote line will extend blockquote:

    > Some text|

<kbd>Enter</kbd>

    > Some text
    > |

You didn't mean it? Press <kbd>Enter</kbd> again:

    > Some text
    |

The feature will work with lists, too:

    > * Some list item|

<kbd>Enter</kbd>

    > * Some list item
    > * |

or:

        >         * Some indented list item|

<kbd>Enter</kbd>

        >         * Some indented list item
        >         * |

As a detail, list indent feature works in blockquotes, too:

    > * Some list item
    > * |

<kbd>Tab</kbd>

    > * Some list item
    >     - |