rm tmp files + add gitignore

Two things:

- I added a .gitignore file to ignore the temporary files created by LaTeX (.aux, .log, .out...), there's no reason to put these files in the git repo. You can copy this file and use it in all your git repositories, it can also be used to ignore entire folders, specific files, etc...

- Most of your equations in your LaTeX file have a label (which is good) but then you write "Equation 9" in the text. You can use the labels with the \ref command, i.e.: "Equation \ref{somelabel}". It's nice because when you add new equations you don't need to spend hours (or months!) renumbering the equations in the text.