Some documentation improvement

[user202729]

Not sure if all are desired. Feel free to cherry-pick some.

Side question: is there any reason why the current @node statements explicitly specify the next/prev/up link? According to texinfo documentation:

You may optionally follow the node name argument to @node with up to three optional arguments on the rest of the same line, separating the arguments with commas. These are the names of the ‘Next’, ‘Previous’, and ‘Up’ pointers, in that order. Hence, the template for a fully-written-out node line with ‘Next’, ‘Previous’, and ‘Up’ pointers looks like this:

@node node-name, next, previous, up

The node-name argument must be present, but the others are optional. If you wish to specify some but not others, just insert commas as needed, as in: ‘@node mynode,,,uppernode’. Any spaces before or after each name on the @node line are ignored. However, if your Texinfo document is hierarchically organized, as virtually all are, we recommend leaving off all the pointers and letting texi2any determine them.

Thus I delete some of the links in some @node elements.

Closes #425.

[johncbowman]

The node links are autogenerated so let's leave them as they are.