Fix typo in schemes.tex

Thanks to Anfang
http://stacks.math.columbia.edu/tag/0356#comment-651
Add brackets in topology.tex

Thanks to Wei Xu
http://stacks.math.columbia.edu/tag/09UW#comment-652
Fix typo in cohomology.tex

Thanks to Fan
http://stacks.math.columbia.edu/tag/01EA#comment-653
Fix typo in homology.tex

Thanks to Fan Zheng
http://stacks.math.columbia.edu/tag/011G#comment-654
Replace 'etc, et'c by 'and so on'

Thanks to Anfang Zhou
http://stacks.math.columbia.edu/tag/01JW#comment-655
Fix typos in topology.tex

Thanks to Wei Xu
http://stacks.math.columbia.edu/tag/0A2P#comment-656