Pdf-maker

* Add rotation attribute for text item (might also work for other items like rect).
* Change the priorities of three rich text tags, now color > super/subscript > break. That means
<red>AB_CD<r>EF<red> is allowed, but AB_{<red>CD</red>} will be not displayed correctly.
And these tags should not separate others, like <red>_CD</red>, which will be displayed wrong.

* Try to embed font files into the Font Descriptor objects.
[This answer](https://stackoverflow.com/a/76125971/22143697) show an example of embedding font files,
his pdf works well in Adobe Acrobat. But I failed to do this, still trying to fine why.
* For reference, [This answer](https://stackoverflow.com/a/3489099/22143697) introduced how to extract
font info from a pdf file.
* This issue haven't been solve.

* Fix font issue, currently Arial font works well, Adobe can successfully recognize the texts,
but other fonts may not work for Adobe Acrobat. Adobe Illustrator can work well for all fonts.
* Add auto middle alignment for tests.

* Add other attributions such as FontDescriptor in the Font object.
* Read font information from xml files, and embed them into the pdf.
* A horizontal scale (integer) will be used to control the actual widths of characters, default 0.5.

* Add canvas

* First release
* Basic functions: Create a PDF, add text, lines and scatters. Supports superscript
and subscript and different color in one string.