Spacing
New functions, search_for_{crop,mineral}().  Takes a string as a parameter, and returns the first crop/mineral whose name contains that string (e.g. pass "eat" and get CROP_WHEAT back).
General cleanup.  Include crop/mineral name in progress popups.  Simplify add_resource() (no need to check if the resource is already there if we're using bitwise or).  World_map::draw() now allows you to press c (for crop) or m (for mineral), enter a (partial) name, and have all tiles that contain that resource highlighted.  Pressing t turns off all highlighting.  Fixed the ? command; it was looking at resources at the top-left corner, NOT under the cursor!  The command now also tells you the position of your cursor and the "code" (int value) of the crops/minerals there.