Check tables exist before creating

Props @ericjuden
Fix importer

Fixes #6
Merge pull request #9 from johngodley/fix/importerror

Fix importer
Merge pull request #8 from johngodley/fix/tablecreation

Check tables exist before creating
Bump versions ready for release
Consistently use the same filter for required user capabilities

In redirection.php, line 130:
apply_filters( 'redirection_role', 'administrator' )
is used so that the required capabilities for using 'Redirection' can be modified without modifing the plugin itself.

I think that the same filter should be used in ajax.php
Merge pull request #11 from RodGer-GR/patch-1

Consistently use the same filter for required user capabilities
Merge master into pagers