Fix link typo in render-documents.adoc

Typo in link to asciidoctor-fopdf.
Merge pull request #147 from peterkuma/master

Fix link typo in render-documents.adoc
expands substitutions and passthrough sections

- adds examples for custom substitutions
- adds passthrough examples and descriptions
- reorganizes controlling content section
- moves literal, listing, and open block sections
- related to issue #91
Merge pull request #148 from graphitefriction/custom-subs

expands substitutions and passthrough sections
closes #149 updates toc syntax from toc2 to :toc: left

- updates toc preferences in user manual toc section
- updates example in attribute section of user manual
- updates toc info in writers guide
- removes toc2 examples
- adds toc left examples
- changes example file names
Merge pull request #150 from graphitefriction/toc2-sidelining

closes #149 updates toc syntax from toc2 to :toc: left
resolves #152 organizes basic API and CLI usage in manual

- moves information to includes
- creates API part in user manual
- expands usage quick start sections
- checks command line reference format
Merge pull request #153 from graphitefriction/api-cli-org

resolves #152 organizes basic API and CLI usage in manual