apt.8: summarise remaining verbs (Closes: #827785)

The following were undocumented:

// package stuff
{"auto-remove", &DoInstall, nullptr},
{"autopurge",&DoInstall, nullptr},

// system wide stuff

// misc
{"moo", &DoMoo, nullptr},

// for compat with muscle memory
{"dist-upgrade", &DoDistUpgrade, nullptr},
{"showsrc",&ShowSrcPackage, nullptr},
{"depends",&Depends, nullptr},
{"rdepends",&RDepends, nullptr},
{"policy",&Policy, nullptr},
{"build-dep", &DoBuildDep,nullptr},
{"clean", &DoClean, nullptr},
{"distclean", &DoDistClean, nullptr},
{"dist-clean", &DoDistClean, nullptr},
{"autoclean", &DoAutoClean, nullptr},
{"auto-clean", &DoAutoClean, nullptr},
{"source", &DoSource, nullptr},
{"download", &DoDownload, nullptr},
{"changelog", &DoChangelog, nullptr},
{"info", &ShowPackage, nullptr},

And there's good reason for some of it, but I unironically didn't know where apt changelog lived. It's unsearchable.

So the following are now simple links with no paragraphs:

// query

// package stuff

// system wide stuff

// misc

// for compat with muscle memory
{"showsrc",&ShowSrcPackage, nullptr},
{"depends",&Depends, nullptr},
{"rdepends",&RDepends, nullptr},
{"policy",&Policy, nullptr},
{"build-dep", &DoBuildDep,nullptr},
{"clean", &DoClean, nullptr},
{"distclean", &DoDistClean, nullptr},
{"autoclean", &DoAutoClean, nullptr},
{"source", &DoSource, nullptr},
{"download", &DoDownload, nullptr},
{"changelog", &DoChangelog, nullptr},