docs: Add troubleshooting.md.
Merge pull request #49 from memmett/feature/add-troubleshooting

Add troubleshooting guide.
encap: Provide default implementation of mat_apply.
Untabify.
Merge pull request #50 from memmett/feature/default-mat-apply

Provide default implementation of `mat_apply`.
reordering tests for examples into subfolder
Merge pull request #52 from torbjoernk/feature/reorder-tests

reordering tests for examples into subfolder