Change the representation of matrices

The code is only partially changed; it will not compile
Doesn't work yet
Continuing rewrite; still not finished
It compiles
Install test binaries too (so they can be debugged)
Cleanup representation
Fix initialization mistake
cppcheck and tidying
Fix memory management bug
Fix test-matr bug: missing indirection
Compile original rnc.cpp; Also, g_thread_init has been deprecated
Deny copying Matrix objects (Known bug: no deep copy ==> double free())
Remove useless Matrix initialization code
Add function: copy to contiguous memory area
Fix bug in invert()
Fix bug caused by Matrix object copying
Use Element instead of fq_t
Fix saving matrices into files
Fix compile error: `md` not declared
Fix generating random matrices (do not reinitialize the seed)