Merge pull request #262 from Morphan1/master

Added <util.random.element[string_list]> to show a random string
Make Shoot command shoot sand blocks by default when falling_block is used as the entity. Preparing to allow other kinds of blocks.
Rename Walkto command into Walk.
Add <player.flag[flag_name]> and <npc.flag[flag_name]> to return a dList of the flag values.
Merge pull request #263 from Morphan1/master

Added 'random' attribute to dLists
Add boolean constructer to Element. Add 'abs' and 'length' attributes to Element. Add flag-dList specific tags 'is_expired'
Make dEntity allow Entity
Fix build due to dEntity change. Make dColor use static Random.
Fix dScript argument matching.
Make Shoot command use new argument system. Example syntax: - shoot source:p@davidcernat projectile:falling_block
Simplify dEntity regex.