Implement support for new JMdictDB <example> element

[machinamentum]

Sometime in 2021, the JMdictDB project added back in examples in a new format.
DTD reference: https://gitlab.com/yamagoya/jmdictdb/-/blob/master/jmdictdb/data/dtd-jmdict.xml

There are ~30k example sentence pairs (described as "priority", whatever that means) imported from tatoeba.

Using these sentences requires rebuilding the jamdict database with JMdict_e_examp.gz found at https://web.archive.org/web/20250401012724/https://www.edrdg.org/wiki/index.php/Main_Page in place of JMdict_e.gz. As of writing this, JMdict_e_examp.gz from archive.org has creation date of 28 March 2025.
It looks like it is also relatively straightforward to generate the latest JMdict_e and JMdict_e_examp XML files using the tooling from the JMdictDB project, see https://gitlab.com/yamagoya/jmdictdb/-/blob/master/doc/OPERATION.txt

This change adds:

• a new SQL element type, SenseExample with entries for "jpn" and "eng" sentence pair
• a new python class, SenseExample
• parsing support for <example> element
• Printing examples under their associated sense, via lookup.py

Example output from lookup.py:

(penv) machinamentum@MacBook-Air jamdict % python3 jamdict/tools.py lookup 食べる
========================================
Found entries
========================================
Entry: 1358280 | Kj:  食べる, 喰べる | Kn: たべる
--------------------
1. to eat ((Ichidan verb|transitive verb))
	1. もっと果物を食べるべきです。
	   You should eat more fruit.
2. to live on (e.g. a salary)/to live off/to subsist on ((Ichidan verb|transitive verb))
	1. 僕は脚本家で食べていく決心をした。
	   I am determined to make a living as a playwright.

========================================
Found characters
========================================
Char: 食 | Strokes: 9
--------------------
Readings: shi2, si4, sig, sa, 식, 사, Thực, Tự, ショク, ジキ, く.う, く.らう, た.べる, は.む
Meanings: eat, food

Char: 喰 | Strokes: 12
--------------------
Readings: shi2, si4, sig, 식, Thặc, Thực, Tự, く.う, く.らう
Meanings: eat, drink, receive (a blow), (kokuji)


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[machinamentum]

This maybe closes #18 even though this change does not parse and store the examples directly from tatoeba.