changes to build without warnings on macOS in December 2021 (and fixes #31 & #33)

[gingerbeardman]

With latest build tools there was a LaTeX error. See: https://github.com/greyscalepress/manifestos/issues/38

To workaround LaTeX error:

• I removed line 137 \setmainlanguage{$mainlang$}

This builds, with warnings. 🤔

Next, to clear the warnings:

• Remove U+0090 character from "Once upon a time�" in 2007-avant-pop.md
• Changed 中国电信 to China Telecom in 2015-01-new-clues.md

This builds, without warnings. 👏

My build process:

1. install included fonts to macOS Font Book.app (so I revert a font define to HKGrotesk-Regular in build.sh) (fixes #31)
2. install required LaTeX extensions (see README)
3. terminal:

   cd scripts
   chmod +x build.sh
   ./build.sh

Bonus:

• added .epub generation to address #33