Add manual skeletion

Skeleton with outline, copyright blurp and TeXInfo metadata
Add introduction section

This section explains features, installation and activation.
Add descriptions for top level menu
Add commands to compile documentation

Test documentation building on Travis CI.
Add Usage intro and selection section
Add macro and index for syntax checkers
Wrap overlong line
Add checker configuration section
Add an appendix listing all checkers
Fix menu alignments
Add indices
Fix cross reference
Remove reference to customization
Add section about error reporting
Add credits and drop help node
Improve usage chapter
Drop customization chapter and add error analysis section
Refine command and option documentation
Document error navigation
Add outline for contributing section