Fix typos and text errors in example notebooks

[tcz]

I found a few typos and inconsistencies when I looked through the example notebooks in this repo. Here I fixed what I found.

• introduction: fix "have have", "explaination", "use use", "a targeted benchmarks", and update chain/draw counts to match code (3/100)
• grokking: fix "We'll starting off", "So let's a point", duplicated "change in LLC" phrase, and epsilon value (0.03 -> 0.003) to match code
• dlns: fix "does not show actually reproduce"
• epsilon_beta: fix "master thesis" -> "master's thesis"
• mnist: fix "emtpy_func" typo in function name
• sgld_calibration: fix LaTeX notation (1e^{-n} -> 10^{-n}), fix section numbering (was skipping 4)