type check of relations
added test
Check for empty string.
Fix bug with routing and dashes.
Add @throws fo dock block function signature
@return string was removed by error
Check for file existence.
Merge branch '4.0'
Merge pull request #2769 from semalead/throws

Add @throws docblocks to many functions
Merge pull request #2734 from anlutro-pull-requests/relationship-type-check

Type check of relations
Tweaking some code.
Use proper instance of Relation

Bugfix from @anlutro's recent PR #2734
Merge pull request #2771 from adamgoose/master

Use proper instance of Relation
Fixed typo
Merge pull request #2773 from billmn/master

Fixed typo
Remove strtolower(), already done in snake_case()
Merge pull request #2782 from PhiloNL/fix/strtolower-snake-case

Remove strtolower(), already done in snake_case()
Blade blade.compiler separate from engine.