fixing invalid escape sequences in various places

[fchapoton]

all remaining cases outside of homology and interfaces folders

CC: @tscrim

Component: documentation

Author: Frédéric Chapoton

Branch/Commit: dbfde86

Reviewer: Travis Scrimshaw

Issue created by migration from https://trac.sagemath.org/ticket/26132

[fchapoton]

New commits:

dbfde86

py3: fix some remaining invalid escape sequences

[fchapoton]

Branch: u/chapoton/26132

[fchapoton]

Commit: dbfde86

[fchapoton]

comment:3

ok, bot is morally green, please review

[tscrim]

Reviewer: Travis Scrimshaw

[tscrim]

comment:4

LGTM.