Check of xsendfile is available.
Add custom filter of tags in the OPDS feed using facets.

Need more testing but should be ok.

re #21
With FBReaderJ 1.6.9 the problem with OPDS search is fixed

See https://github.com/geometer/FBReaderJ/issues/70
Add first file to make use of custom columns. Not complete at all.

re #32