Save all metadata from the entries.

So far when you update an entry, some of the metadata from the entry
like the location and the weather were removed from the entry. This
fixes it.
Do not save empty location in entries.

Prevents weird glitch in the iOS version of Day One.
Do not save empty optional metadata.
Merge pull request #4 from aliou/metadata

Save all metadata from the entries.
Bumped version
added sanity checking to file system operations
added assertion on save step of the remove() unit test - this hid an error where the entry was not saved because of lack of fs sanity checking
Merge pull request #6 from StephenCWan/master

Added support for filesystem sanity checking
bumped version