v0.30: core restructuring and unit tests

* Complete rewrite of BackRest::File module to use a custom protocol for remote operations and Perl native GZIP and SHA operations.  Compression is performed in threads rather than forked processes.

* Fairly comprehensive unit tests for all the basic operations.  More work to be done here for sure, but then there is always more work to be done on unit tests.

* Removed dependency on Storable and replaced with a custom ini file implementation.

* Added much needed documentation (see INSTALL.md).

* Numerous other changes that can only be identified with a diff.