Add a / to the beginning of a file matchin pattern if no / in rule.

See https://www.kernel.org/pub/software/scm/git/docs/gitignore.html
Add note about package naming in VCS repos/fork, fixes #1761
Update 02-libraries.md

Missing word
Merge pull request #1764 from simonpaarlberg/patch-1

Update 02-libraries.md
Merge pull request #1754 from njam/issue-1754

Fix file pattern start matching if no slash
Fix normalization of relative paths going up a few dirs, fixes #1759
Fix undef var issue when removing a json config key