Leidenmark

Glyph processor added for `*chiro*`, `*slanting-stroke*`, `*tripunct*` and `*leaf*`. Cf.: http://papyri.info/docs/leiden_plus#special-characters

This release includes several new processors for broader Leiden+ support, as well as some bugfixes to old ones. The new processors are listed below, linked to the corresponding sections on http://papyri.info

[Special characters](http://papyri.info/docs/leiden_plus#special-characters)

1. Paragraphos: `----`

[Marginalia](http://papyri.info/docs/leiden_plus#marginalia)

1. Text inserted / added above line: `\ὅλων/`
2. Text added between lines: `||interlin: ὧν||`

[Other editorial conventions](http://papyri.info/docs/leiden_plus#other-editorial-conventions)

1. [Handshift](http://papyri.info/docs/leiden_plus#handshift): `$m4`

Extras (Not yet on papyri.info)

1. Diples:

To get this PN preview: (diple)
Use this Leiden+: ((diple))
<milestone rend="diple" unit="undefined"/>

2. Eisthesis (indentation):

To get this PN preview: line in eisthesis
Use this Leiden+: (1, indent)
To create this XML: <lb n="1" rend="indent"/>

This release includes:
* A `pytest` integration and some first basic tests
* A new, decentralized processor registration system. Each submodule now has a register function (e.g. `register_divisions` in `divisions.py`) that registers the corresponding processors. These functions can also be imported when building a custom extension using this package. Note that individual processors should be imported from their submodules (e.g. `from leidenmark.divisions import DivisionsPreproc` instead of the former `from leidenmark import DivisionsPreproc`).