Notes from the original PR:

The dependencies for android in autobuild can not be installed in
pdf-tools-install, they have to be installed manually in Termux. But
the dependencies are checked when running autobuild.

pdf-tools-install successfully installs epdfinfo in Android Emacs. One
can then view pdf files.

The shebang in autobuild does not work in Termux, I therefore had to
create a separate script "autobuild.android" that in turn executes
autobuild. The problem with the shebang is that "env" in Termux is not
located at "/usr/bin/env".

pdf-tools/Makefile does currently not work in Android Emacs, but it is
not needed for running pdf-tools-install. Fixing this will have to be
done in a separate pull request, if deemed necessary. Reason: There is
yet no consensus for how to implement a command line emacs, to be run
in batch mode, in Android Emacs.

I have successfully run "make test" in Ubuntu, in the repo feature
branch. Running "make server-test" in the master branch fails, so I
have not tested this in the feature branch.

Closes: #230
Author: @johanwiden