devel: Add lua-cov

LuaCov is a simple coverage analyzer for Lua scripts. When a Lua script is
run with the luacov module loaded, it generates a stats file with the number
of executions of each line of the script and its loaded modules. The luacov
command-line script then processes this file generating a report file which
allows one to visualize which code paths were not traversed, which is useful
for verifying the effectiveness of a test suite.


(nia)