S7 Integration for GNU TeXmacs 2.1.1

[da-liii]

The pull request is adapt from mgubi/texmacs#5

Build

Build: Using CMake on GNU/Linux

mkdir build && cd build && cmake -DCMAKE_INSTALL_PREFIX=$HOME/software ..
make -j8
make install -j8

Testing

Launch the built TeXmacs via:

$HOME/software/bin/texmacs

Note

The author of this PR is Massimiliano Gubinelli (@mgubi) .

Joy Yang (@326623) and Darcy Shen (@darcy-shen ) are making improvements based on @mgubi 's work.

[mgubi]

Why this pull request? At this moment I do not think we want to switch to s7 right away. I think it is better to keep a branch with the s7 code in this repository, so that users which want can use it. I will drop the branch on my repository and move my development here. I've created a branch 'texmacs/wip_s7'. Shall we use it? It contains all the changes and then updated S7 to the last version.

[da-liii]

OK, let me close it.