Merge pull request #9 from demon386/master

Bugfix for `ebib-find-bibtex-entries` when unknown entry type is encountered.
Fixed docstrings.
Fixed two defcustoms.
helm-bibtex-bibliography: Allow file or list.

Mainly for backward-compatibility.
Merge branch 'multi-bibtex'

Allow multiple bibliographies, i.e. multiple BibTeX files.
Merge branch 'master' of https://github.com/tmalsburg/helm-bibtex
Added multiple bib-files to list of features
Added docstring to `helm-souce-bibtex`.
Rename helm-bibtex-init to helm-bibtex-candidates.
Extended description of `helm-bibtex-bibliography`.
Generate edit-actions for each BibTeX file.
Typos.
Check that BibTeX files exist and

produce an error message otherwise.
Add the ability to format bibtex key when inserting.