make mime types configurable
fix comment typo
remove not null constraint
update README with mime types example configuration
Revert "fix comment typo"

This reverts commit ae24d92b384ccc1bd5261ed3f05b1d9bd21e87da.
Revert "remove not null constraint"

This reverts commit 32f5c29a23341c4f1dd6c1241a751201ce286430.
 - apply custom mime mappings in separate method
 - add test case
Merge pull request #16 from akoskm/mimeTypes

make mime types configurable