Move grd_lib out of clua.cc into l_mapgrd.cc.

Rest of commit comment only as accurate as my understanding…

Renaming from grd to mapgrd to avoid confusion with grd == env.grid: This grd is the maplines-section of a vault definition.

Also move mapgrd_lib from clua to dlua since it's only used for dungeon building.

clua and dlua need more descriptive names.

Created by  Robert Vollmert  on October 20, 2009
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