v1.0.0 release


### Changes

* `move(n)` moves forward by n entries if n is positive, backwards otherwise.
* `filter` adds a series of filters to the journal, restricting what is returned when iterating.
* Journal now implements enumerable.  `each` will iterate over all items in the journal matching the current filters.
* `add_match`, `clear_matches` are now `add_filter`, `clear_filters`.
* `current_entry` now returns a `JournalEntry` object instead of a hash (but will still respond to hash access).
* `watch` will call it's block whenever the journal changes.
* `Systemd::Journal.perror(message)` now exists.
* `wait` now returns `nil` instead of `:nop` if no new entries were written.
* `cursor` returns a string that can be passed to `seek` to return to a given entry
* `cursor?(c)` returns true if we are at the entry described by the cursor `c`.
* `data_threshold` and `data_threshold=` gets/sets the maximum size of data to be returned for a field.
* all journal field names can now be symbols or lowercase strings; they will be converted to uppercase prior to calling native functions.