initial tex file with example cake

[Necktschnagge]

Travis stuff was checked and is nmow working properly to

• get a failed job on wrong tex syntax
• get a failed job on bad boxes warnings (and possible other warnings...)

[Necktschnagge]

I put Travis stuff in extra PR already merged: #2

[Necktschnagge]

• opened an equivalent PR here #4
• closing this one