Add bibliography chapter

Signed-off-by: trivernis <trivernis@protonmail.com>

chapters/bibliography.md

@@ -0,0 +1,71 @@
+# Bibliography
+
+Snekdown Supports Bibliography entries and references similar to BibTex.
+
+Definition:
+```
+[SD_GITHUB]: https://github.com/trivernis/snekdown
+[SD_BOOK]:[type=book, author=Snek, title = "Snekdown Book" date="08/20/2020", publisher=Snek]
+```
+
+[SD_GITHUB]: https://github.com/trivernis/snekdown
+[SD_BOOK]:[type=book author=Snek, title = "Snekdown Book", date="08/20/2020" publisher="Snek "]
+
+The definitions of bibliography entries are not rendered. Instead the `[[BIB]]` placeholder 
+must be used to insert a table of bibliography entries. Only entries that are used in the document are rendered.
+
+[[BIB]]
+
+To reference a bib entry, use the `[^KEY]` syntax. For example:
+`[^SD_BOOK]`.
+This renders as [^SD_BOOK].
+
+
+The numbers are assigned based on first occurrence.
+```
+There is a book about snekdown[^SD_BOOK] and a github repo[^SD_GITHUB].
+```
+
+There is a book about snekdown[^SD_BOOK] and a github repo[^SD_GITHUB].
+
+
+The bibliography handling is provided by the [Bibliographix](https://github.com/Trivernis/bibliographix) crate.
+Supported types are:
+
+
+| Type          | Required Fields                               | Optional Fields                                    |
+| ------------- | --------------------------------------------- | -------------------------------------------------- |
+| article       | key, author, title, journal, date             | volume, number, pages, url                         |
+| book          | key, author, title, publisher, date           | volume, series, address, edition, url              |
+| booklet       | key, title                                    | author, how_published, address, date               |
+| in_book       | key, author, title, position, publisher, date | volume, series, address, edition                   |
+| in_collection | key, author, title, publisher, date           | editor, volume, series, position, address, edition |
+| manual        | key, title                                    | author, organization, address, edition, date       |
+| misc          | key                                           | author, title, date, url, how_published            |
+| repository    | key, author, title                            | url, cms, license, accessed_at                     |
+| tech_report   | key, author, title, institution, date         | number, address                                    |
+| thesis        | key, author, title, school, date              | address                                            |
+| unpublished   | key, author, title                            | date                                               |
+| website       | key, url                                      | title, author, accessed_at, date                   |
+
+ 
+Bibliography can also be defined in a separate TOML file with the following syntax:
+
+```toml
+# Bibliography.toml
+[BIB_KEY]
+key = "value"
+
+[SD_BOOK]
+type = "book"
+author = "Snek"
+title = "Snekdown Book"
+date = "20.08.2020"
+publisher = "Snek"
+
+[SD_GITHUB]
+type = "website"
+url = "https://github.com/trivernis/snekdown"
+```
+ 
+

main.md

@@ -39,4 +39,8 @@
 
 - - - 
 
-<[chapters/images.md]
+<[chapters/images.md]
+
+- - -
+
+<[chapters/bibliography.md]