Add matlab and lyx run scripts and examples

[lucamlouzada]

This issue is part of an effort to implement substantive improvements to the lab template, as discussed in https://github.com/gentzkow/GentzkowLabTemplate/issues/16.

In this issue, the goal is to add examples, run_xx scripts and instructions for MATLAB and Lyx.

I am assigning myself to work on this. Because the make.sh and run_xx scripts were changed in #18 to improve error handling, this issue should only be closed after #18 and the associated PR #19 are closed, so that the new run_xx scripts are standardized with the other versions. I will start by creating the scripts following the initial commit in #19, and it will be necessary to update them afterwards in case there are any changes during the review.

[lucamlouzada]

I have pushed several changes to this branch.

• In fbc1bb6, I introduced the run_matlab.sh command, which follows the structure in the other run_xx scripts pushed in #19. Running it requires that MATLAB is properly installed and added to path for command line usage.
• In e594e5a, I added two example scripts for data wrangling and analysis with MATLAB, following the exact same pattern as the scripts in R, Python and Stata
• In 7c96bca, I introduced the run_lyx.sh command, which follows a similar structure to the run_latex version pushed in #19. One important difference is that Lyx is called with the full path to prevent issues that happen due to the way Lyx handles environments in the command line when converting .jpg objects to pdf. A minor fix to comments in this script was added in a881c10.
• In 5d1fdd2 and 5c2603b, I pushed example Lyx scripts for compiling an example paper and slide deck, closely following the Latex examples.

• In 063fe83, I copied the .bib file from the examples/latex folder to the examples/lyx folder, so that users know that they should copy that file to 4_paper/source if they want to compile a paper using Lyx

  I have not added instructions yet because I believe they should be standardized with the instructions for R, Python and Stata which depend on the current approach for error handling being approved in #19. Therefore, README files will be updated in a future step.