#20 Allow LocalDate to be serialized/deserialized as number (epoch day)

[kewne]

Fixes #20

[cowtowncoder]

Ok, sounds good to me.
Have I already asked for a CLA? If not, I'd need one from:

https://github.com/FasterXML/jackson/blob/master/contributor-agreement.pdf

and usually easiest way is to print, fill & sign, scan, email to info at fasterxml dot com.
Only needs to be done once, good for any number of contributions.

If this could be done, I can merge this in; seemed good to me (I'll add comments if I have any, so far I don't).

[cowtowncoder]

Received CLA, merging.