This tool is intended to be used to create an epub version of the
standard documentation.

An epub is just a .zip file containing a bunch of XHTML files and
a few files containing metadata.

Our structure will look like:

    Book Root Directory
      |-- META-INF directory
      |         `-- container.xml
      |-- mimetype
      |-- content.opf
      |-- toc.ncx
      |-- stylesheet.css
      |-- cover.xhtml
      |-- toc.xhtml
      |-- chapterAA.xhtml
      |-- ...
      `-- chapterZZ.xhtml


Begin by defining some helper functions for writing to a
file.

~~~
'FID var
:file:s:put [ @FID file:write ] s:for-each ;
:file:nl    ASCII:CR @FID file:write ;
:unix:mkdir 'mkdir_-p_%s s:format unix:system ;
~~~

Create the directories needed.

~~~
'epub unix:mkdir
'epub/META-INF unix:mkdir
~~~

Then create the `mimetype` file. This is supposed to be written
without a trailing newline.

~~~
'application/epub+zip 'epub/mimetype file:spew
~~~

Then create `META-INF/container.xml`.

~~~
'epub/META-INF/container.xml file:open-for-writing !FID

  '<?xml_version="1.0"?> file:s:put file:nl
  '<container_version="1.0"_ file:s:put
  'xmlns="urn:oasis:names:tc:opendocument:xmlns:container"> file:s:put file:nl
  '<rootfiles> file:s:put file:nl
  '<rootfile_full-path="content.opf"_ file:s:put
  'media-type="application/oebps-package+xml"/> file:s:put file:nl
  '</rootfiles> file:s:put file:nl
  '</container> file:s:put file:nl

@FID file:close
~~~

Create `content.opf`. This will need to lest all of the files
that are used in the book.

Todo:

- verify the required fields and metadata
- write this to a file

  <?xml version="1.0" encoding="utf-8" standalone="yes"?>
  <package xmlns="http://www.idpf.org/2007/opf" unique-identifier="BookID" version="2.0">
    <metadata xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:opf="http://www.idpf.org/2007/opf">
      <dc:title>RETRO Forth : User Manual</dc:title>
      <dc:identifier id="BookID" opf:scheme="CustomID">...bookid...</dc:identifier>
    </metadata>

    <manifest>
      <item href="chap01.xhtml" id="chap01_page" media-type="application/xhtml+xml"/>
    </manifest>

    <spine toc="ncx">
      <itemref idref="chap01_page" linear="yes"/>
    </spine>

    <guide>
    </guide>

  </package>

Assemble the pieces

~~~
'epub unix:chdir
'.. unix:chdir
~~~

zip -0Xq /tmp/book.epub mimetype
zip -Xr9Dq /tmp/book.epub *

Cleanup is the final step. Remove the temporary epub directory

~~~
'rm_-rf_epub unix:system
~~~