-Update: bring Doxygen file tags up to date
-Codechange: missed a few SCREEN conversions
-Codechange: declare some functions and variables static
-Codechange: convert function declarations to prototypes
Merge pull request #167 from wangds/cleanup

-Update: bring Doxygen file tags up to date
-Codechange: missed a few SCREEN conversions
-Codechange: declare some functions and variables static
-Codechange: convert function declarations to prototypes
-Codechange: it is called an MCV (patch by wangds)
-Change: give some credit where credit was more than due
-Codechange: use enums for buildableUnits (based on patch by wangds)

On that note, it can be an uint8; this way -1 is UNIT_INVALID again.
-Codechange: missing space (yes, those things annoy me)
-Codechange: use enums for structuresRequired  (based on patch by wangds)

FLAG_STRUCTURE_NEVER is a bit special, but by the lack of a better name
it will have to do.
-Fix: forgot to add doxygen comments where needed
-Codechange: use enums for availableHouse (patch by wangds)
-Codechange: use enums for enterFilter (based on patch by wangds)
-Codechange: use enums for bulletType (based on patch by wangds)
-Fix: select the structure when a unit enters (patch by wangds)
-Fix: remove fog of a structure around its center (patch by wangds)
-Fix: only show spice field hint when a harvester is deployed (patch by wangds)
-Codechange: remove orientation table (patch by wangds)
-Codechange: make g_table_landscapeInfo const (patch by wangds)
-Codechange: delay House_Get_ByIndex when possible