Added a SEED iuse function so you do not eat hemp seeds by accident.

Updated documentation about how to add new iuse functions.
Bindle and Sling

Some simple and easy carrying devices.
Alters spike recipe to account for size of materials.

It was using nine volume worth of metal to produce a particularly simple
single volume item. This reduces it to three for one.
Trying to fix the jenkins error.
Merge branch 'master' of https://github.com/CleverRaven/Cataclysm-DDA into You_Eat_The_Seed
Changes input quantities, removes combat knife from recipe.

Seriously, there's no good reason to *ever* do that to your combat
knife!
Gives a few more material options when constructing a palisade wall.
Merge some item and recipe tweaks.
Merge warning iuse to hemp seeds and primitive storage items.