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

Add troubleshooting guide.
Merge pull request #50 from memmett/feature/default-mat-apply

Provide default implementation of `mat_apply`.
Backmerge branch 'development' into feature/mpi-pf

* development:
  Untabify.
  encap: Provide default implementation of mat_apply.
  docs: Add troubleshooting.md.
  creating CHANGELOG file

Conflicts:
	include/pfasst/encap/encapsulation.hpp