Fix broken links in documentation

[aedwardg]

Several of the links in the documentation were broken or pointed to the wrong place (mostly due to re-organized files and changed headings).

All links in the docs should be up to date after this PR.

Code review checklist

• [x] Pull request represents a single change (i.e. not fixing disparate/unrelated things in a single PR)
• [x] Title summarizes what is changing
• [x] Commit messages are meaningful (see this for details)
• [x] Tests have been included and/or updated
• [x] Docstrings have been included and/or updated, as appropriate
• [x] Standalone docs have been updated accordingly
• [x] Changelog(s) has/have been updated, as needed (see CHANGELOG.md, no need to update for typo fixes and such).

[coveralls]

Coverage remained the same at 91.044% when pulling 4e3991fcb726e83fb7f36f70ce155dc709b4566e on aedwardg:fix-doc-links into 042c7e195dc8a31091e499312fd4993d44ea241f on igordejanovic:master.

[igordejanovic]

Looks good. Thanks!