Dubify

Long story short:
* kill makefiles
* use dub to create 3 packages (library + 2 examples: interpreter & extending it)
* fix deprecation warnings
* use undead.date and undead.regexp

This includes hot-fix from pull #2.

Advertising on code.dlang.org is left to you ;) It might be a good time to list it as alpha/beta version.
With current setup the library could be used with "dmdscript:engine" dependency line (see ds and ds-ext).