Fix proof lemma tag 0540

Thanks to Wei Xu
http://stacks.math.columbia.edu/tag/0540#comment-672
Three typos

Thanks to Keenan Kidwell
http://stacks.math.columbia.edu/tag/07DR#comment-673
http://stacks.math.columbia.edu/tag/00JC#comment-674
http://stacks.math.columbia.edu/tag/00JL#comment-675
Typo in schemes.tex

Thanks to Anfang Zou
http://stacks.math.columbia.edu/tag/01I3#comment-677
Fix typos and a proof

Thanks to Keenan Kidwell
http://stacks.math.columbia.edu/tag/00JV#comment-678
http://stacks.math.columbia.edu/tag/00K4#comment-679
http://stacks.math.columbia.edu/tag/00KY#comment-680
http://stacks.math.columbia.edu/tag/00L9#comment-681